Sleep duration rebounds quickly after travel. Circadian timing and sleep architecture do not. A practical system for managing jet lag before, during and after the flight.
You May Feel Fine After Two Days. Your Biology May Not.
Most frequent flyers know the feeling all too well.
You land.
You sleep hard on the first night.
By day two, the fog feels like it has lifted, and you convince yourself: “I’m back.”
Is that the actual reality or does science tell us another story?
Firstly, you need to understand that your subjective recovery and your biological recovery are not the same thing.
A major study in SLEEP (2025) analysed de-identified Oura Ring data from 57,240 users across 64,847 trips, covering sleep for 15 days before and 15 days after travel.
It is one of the largest real-world datasets ever used to study travel-related sleep disruption.
Exciting stuff in my world.
The core finding was simple but important: sleep duration recovered quickly, but sleep timing and sleep architecture recovered much more slowly [1].
In other words, you can sleep “enough” before your body clock has actually re-aligned. Because most of us still align with the dated proxy that good sleep is just a matter of duration, we assume everything's fine.
In worlds where performance matters, this isn’t good enough.
The hidden recovery gap
The study found that total sleep time returned to within roughly 12 minutes of baseline after about two days, which is quick. That explains why travellers often feel better quickly. Sleep pressure builds during travel, and the body compensates with a rebound night.
Accumulate then repay.
Also, at that point, as the yardstick you’re using for that improvement is what you felt like 48 hours ago, so it becomes very subjective.
In the study, the same dataset showed that sleep timing had not returned to baseline after 15 days.
You read that right. 15 days, and at that point they stopped measuring……..
Sleep architecture also remained disrupted, especially after eastward travel and after crossing more time zones. REM sleep, wake after sleep onset, and deep sleep were affected differently depending on route and direction [1].
In simplistic terms. You can’t wake up or fall asleep at your usual times, and the quality when you do is terrible.
That distinction matters.
Sleep duration is the headline number most people notice; like I said it has been for centuries. Sleep timing is the circadian system. Sleep architecture is the quality and sequencing of recovery during the night: latency, deep sleep, REM sleep, light sleep and awakenings.
So the practical message is not “you are broken for two weeks.” It’s far more precise:
You may ‘feel’ recovered long before your sleep physiology has fully recovered.
That’s a different level of awareness for the business traveller, athlete, founder, executive or parent flying long-haul and expecting to perform immediately.
Jet lag is not just tiredness
Jet lag disorder is caused by rapid travel across time zones, which creates a mismatch between the internal biological clock and the local clock. It can show up as insomnia, daytime sleepiness, reduced cognitive performance, gastrointestinal disruption, mood changes and general malaise [2]. At this stage, it’s important to note the relationship between travel and social jet lag. From a biological standpoint, a lot of the signals are the same, so a lot of the consequences also match.
A recent CDC Yellow Book chapter reported that 68% of international business travellers experience negative jet lag symptoms regularly [2].
This is why “pushing through” is not always the high-performance answer. It may feel disciplined and aligned with what you’ve been told, but biologically it often means stacking decision-making, meetings, alcohol, caffeine and artificial light on top of an already misaligned system.
For occasional travellers, this might be uncomfortable. For frequent travellers, the effects can accumulate, contributing to a myriad of health challenges.
We already know that repeated circadian disruption has been associated with higher cortisol levels and cognitive deficits in studies of airline cabin crew, particularly when long-term, repeated transmeridian travel is involved [8].
I was recently asked by one of the major private airlines to compile all this data and propose a practical, low-cost mitigation plan.
“Not right now,” was their response.
Make what you want of that.
The aircraft cabin adds a second stressor
Many travellers call everything they feel after a flight “jet lag.”
It’s too simplistic and often isn’t the case.
A long-haul flight produces at least two overlapping problems:
First, circadian misalignment: your body clock is out of sync with the local (destination) time.
Second, travel fatigue: sleep loss, early wake-ups, disrupted in-flight sleep, cabin pressure, dry air, noise, immobility, alcohol, caffeine timing and stress.
The 2025 Oura dataset found that sleep disruption often began before take-off, with the night before travel already shortened, often because of early waking for flights [1].
That means many travellers aren’t starting the trip neutral. They are starting with sleep debt.
That could be simply starting the process with a red-eye, having a couple of alcoholic drinks at the airport, or simply not being adequately hydrated before they even begin their journey/
“Most people begin a flight already physiologically compromised, carrying sleep debt, circadian disruption, and reduced recovery capacity before wheels-up.”
Cabin pressure: mild hypoxia, not a neutral environment
Commercial aircraft cabins are not pressurised to sea level. The UK Civil Aviation Authority notes that commercial cabins are typically equivalent to about 5,000-7,500 feet, with a regulatory ceiling of 8,000 feet in normal operation. At 8,000 feet, arterial oxygen saturation in healthy travellers can fall to around 90% [3].
A large hypobaric chamber (don’t confuse this here with a hyperbaric chamber) study published in the New England Journal of Medicine exposed 502 adults to simulated aircraft cabin altitudes for 20 hours. At 8,000 feet, mean oxygen saturation fell by about 4.4 percentage points, and discomfort increased at 7,000-8,000 feet after several hours [4].
This doesn’t mean healthy travellers are at risk on a typical flight. It does, however, mean the cabin is a mild hypoxic stressor, especially when combined with sleep loss, alcohol, dehydration, illness, sleep apnoea or underlying heart or lung disease. It becomes a contributing factor.
Practical implication: Do not schedule your most important work immediately after landing if you can avoid it. Your body has been sleeping less, breathing in lower oxygen pressure, sitting still and attempting circadian recalibration all at the same time.
Cabin humidity: dry enough to matter, but be precise
Cabin air is genuinely dry. Typical aircraft cabin humidity is around 10-20%, compared with roughly 40-50% in many buildings [3].
That dries the eyes, lips, throat, skin and mucous membranes. It can increase thirst and make you feel more fatigued.
However, the strongest aviation-medicine guidance does not support the dramatic claim that low cabin humidity alone causes severe dehydration in healthy passengers. The UK CAA notes that additional insensible fluid loss from low cabin humidity is approximately 150 ml over an 8-hour flight, with no evidence of a major change in plasma osmolality [3].
So the more accurate wording is this:
Cabin air is genuinely dry. Typical aircraft cabin humidity is around 10–20%, compared with roughly 40–50% in many buildings [3].
This can dry the eyes, lips, throat, skin and mucous membranes. It can also increase thirst and contribute to fatigue.
However, current aviation-medicine guidance does not support the more dramatic claim that low cabin humidity alone causes severe dehydration in healthy passengers. The UK CAA notes that additional insensible fluid loss from low cabin humidity is approximately 150 ml over an 8-hour flight, with no evidence of a major change in plasma osmolality [3].
A more accurate interpretation is that cabin dryness does not, in itself, usually cause significant dehydration. However, reduced fluid intake, alcohol, caffeine, sleep loss, long flight duration, mild hypoxia and prolonged immobility can combine to make travellers feel noticeably worse.
Most people also drink less during a flight than they would during a normal day on the ground.
Practical implication: hydration should be viewed as a symptom-management tool, not a magic jet lag cure. Drinking steadily before and during travel can help reduce dryness, thirst and fatigue, especially on longer flights.
HMN24 was formulated with this travel context in mind. Its electrolyte blend, including sodium, potassium and magnesium, is designed to support fluid balance and help maintain hydration when intake may be lower than usual. Taken pre-flight and/or during travel, depending on flight duration, it forms part of a broader jet lag mitigation strategy alongside light exposure, sleep timing, movement, sensible alcohol and caffeine intake and of course the rest of the HMN24 system.
Alcohol: the easiest loss to cut
The old line that “one drink in the air equals two on the ground” is memorable, but not the most scientific formulation.
The stronger evidence is worse.
A study in Thorax (2024) simulated long-haul flight conditions using hypobaric hypoxia equivalent to 2,438 metres. When moderate alcohol was combined with sleep under these cabin-like conditions, median oxygen saturation dropped to 85.32%, heart rate rose to 87.73 bpm, and participants spent over 200 minutes below 90% oxygen saturation during a four-hour sleep opportunity. Deep sleep was also reduced compared with the laboratory control conditions [5].
Don’t trust the evidence?
You can measure it.
You probably don’t need a device to tell you that stacking alcohol, poor sleep, and altitude is a bad idea, but if you want to see what's happening, take a finger top pulse oximeter with you and see for yourself what's happening.
Separately, a 2025 systematic review and meta-analysis found that alcohol changes sleep architecture, delaying REM onset and reducing REM duration. Even low doses, roughly equivalent to 2 standard drinks, negatively affected REM sleep [6].
Practical implication: alcohol is one of the simplest high-impact things to remove from a long-haul flight. It may help you fall asleep faster, but it makes the sleep less physiologically useful.
East is harder than west
Most people adjust more easily when travelling west than east. That is because the human circadian period is usually slightly longer than 24 hours, so the body generally finds it easier to delay the clock than advance it.
CDC travel-medicine guidance gives a useful rule of thumb: the body clock adapts by about 1.5 hours per day when travelling west, but only about 1 hour per day when travelling east [2].
That is why London to New York is usually easier than New York to London, all else being equal.
Flying west asks your body to stay up later.
Flying east asks your body to fall asleep earlier.
Biologically, our body typically prefers the first.
Also worth noting that someone staying out 3 hours beyond their normal sleep time and sleeping in by 3 hours to correct it will take roughly 3 days to re-align physiology. This is what we define as social jetlag.
Practical implication: Protect sleep before eastward travel. If you are flying east across multiple time zones, the two nights before departure are part of the trip, not normal life.
Fatigue is performance-relevant
Sleep loss is not just a wellness issue. It changes performance.
Classic fatigue research found that 17 hours awake can impair performance at a level comparable to a blood alcohol concentration of 0.05%, and 24 hours awake can be comparable to 0.10% [7].
This is not theoretical. In aviation, 84% of cabin crew report fatigue while on duty, 71% say it affects safety-related performance, and 52% report having nodded off in flight. Among international business travellers, 68% report negative jet lag symptoms on a regular basis. Fatigue is not just a comfort issue. It is a performance and safety issue.
For travellers, that matters because long-haul trips often combine early starts, airport stress, broken sleep, time-zone shift and late arrival. A traveller who would never drink before a board meeting may still walk into that meeting biologically impaired by sleep loss. Travel drunk.
Practical implication: the first major meeting after landing should be treated like a performance event. Build in recovery, light exposure, hydration, and a short-nap strategy rather than assuming willpower will compensate.
The Traveller’s Practical Protocol
I’m going to frame this in a couple of ways. I designed the HMN24 system to assist in circadian modulation and, alongside that, the structured mitigation of jet lag.
This combines both the standard steps to take and for those of you already capitalising on our system, how that supports and mitigates the impact.
Before you fly
1. Start the trip two nights early
For eastward travel, move bedtime and wake time earlier by 30-60 minutes per day for two or three days if your schedule allows. CDC guidance supports shifting sleep toward the destination time zone before departure, especially for eastward travel [2].
HMN24 System integration:
Our system follows timings. Alongside the other stabilising factors in circadian modulation, the HMN24 system follows the pattren. As you move everything 30-60 minutes earlier, so does your usage. RISE is taken 30 minutes earlier in the morning to anchor your wake time and support the signal your nervous system receives as you expose the optic nerve to light and initiate your wake cycle. HMN24 Flow and Pre-Sleep also move earlier alongside your afternoon and sleep routines.
2. Bank sleep before a demanding trip
Sleep banking is not a substitute for healthy sleep, but evidence suggests that extending sleep before a period of expected sleep restriction can improve alertness and performance during the restriction period and speed recovery afterwards [10].
Go to bed earlier or nap. Do NOT disrupt your sleep anchor by sleeping in; only move it in accordance with any phase-shifting plan. Stability, in almost all
This is about building physiological reserve, not reacting mid-flight
3. Plan your first day realistically
Avoid placing the most cognitively demanding work immediately after landing, especially after an eastward overnight flight. If a meeting cannot move, reduce other loads: no alcohol, no late dinner, no unnecessary evening commitments.
HMN24 integration:
If unavoidable:
- RISE morning activation on arrival
- FLOW > stabilise afternoon performance
This supports output without over-reliance on caffeine spikes
4. Decide whether to adapt at all
For trips under about 48 hours, do not automatically force adaptation to local time. CDC guidance explicitly notes that maintaining home-based sleep, activity, and eating schedules for short trips may reduce misalignment [2].
I recently travelled to Dubai, for example. My sleep-wake pattern runs on a 6 am-10 pm pattern. In Dubai, it was easier to simply adopt a 9 am - 1 am schedule.
My use of HMN24 there simply follows my UK time and stabilises my home rhythm, not shifts it:
On the flight
5. Switch behaviour to destination time when you board
Set your watch to destination time and time sleep, meals, caffeine and light around the destination clock. This is not symbolic. It is behavioural circadian signalling.
In my previous newsletter, I used the example of Toto Wolff, team principal, wearing two watches for this purpose. You can see this HERE.
HMN24 System integration:
Begin aligning supplement timing with destination rhythm immediately and prior too if you’ve been following a shifting schedule
This turns supplementation into a circadian cue that supports circadian amplitude, not just intake
6. Sleep only when it is sleep time at the destination
If it is night at your destination, create darkness: eye mask, low light, minimal screens, cool temperature, quiet. If it is daytime at your destination, avoid a long sleep that will steal pressure from the first local night.
HMN24 integration:
Use PRE-SLEEP strategically in-flight
Not to force sleep, but to support correct-timed sleep
7. Avoid alcohol
The evidence is now strong enough to make this simple: alcohol plus cabin-like hypoxia worsens oxygen desaturation, raises heart rate and reduces sleep quality [5]. Alcohol also reduces REM sleep [6]
8. Use caffeine strategically, not emotionally
Caffeine can help with alertness, but timing matters. Use it during daytime at the destination and avoid it in the hours before the target bedtime. CDC guidance notes caffeine’s usefulness for alertness but warns about timing because of its sleep-disrupting half-life [2].
HMN24 integration:
Use RISE instead of reactive caffeine use
The caffeine + L-theanine combination supports:
- Smoother alertness
- Reduced jitter
- Improved cognitive control
This is structured stimulation vs chaotic intake
9. Hydrate steadily
Drink water before you feel thirsty, especially if you are drinking coffee, eating salty food or flying after poor sleep. The goal is not to “flush out jet lag.” The goal is to avoid adding headache, dry mouth and avoidable fatigue to the circadian problem.
HMN24 integration:
Use HYDRATE pre-flight and in-flight
Key role:
- Improves fluid retention (sodium-driven)
- Supports electrolyte balance under stress
- Reduces fatigue linked to mild dehydration
Not “hydrating more”
HMN24 Hydrate is formulated to maintain fluid and electrolyte sufficiency in a hypohydrating environment, where loss is subtly but consistently increased.
10. Move every 60–90 minutes
Movement will not reset the circadian clock on its own, but it reduces stiffness, supports circulation, and helps limit the perceptual fatigue you feel on arrival.
Hydration supports this process, not by “adding more,” but by preventing fluid and electrolyte deficits in an environment that promotes them, helping maintain blood volume and circulation.
Compression socks (15–20 mmHg, or up to 20–30 mmHg for longer flights) can further support venous return, reduce lower limb swelling, and improve overall comfort during prolonged immobility.
When you land
11. Get outdoor light early (timed correctly)
Light is the strongest natural circadian cue. As a practical default, get outside as soon as you arrive at your destination if it's landing in that first daytime window. For large time-zone shifts, the optimal timing of light depends on direction and the number of time zones crossed; timed light can either advance or delay the circadian clock [2].
Use a light source, such as the Ayo Blue Light-emitting glasses, and control your own light by packing an eye mask, too.
(Use HMN24 as a code for 20% off).
HMN24 integration:
RISE is designed to be paired with light exposure to modulate circadian rhythm in the morning.
This is critical:
Light = primary circadian signal
RISE = biochemical reinforcement
Together this creates a stronger circadian anchoring
12. Eat on local time
Meal timing is a secondary circadian cue. It will not overpower light, but it helps signal the new day-night structure.
HMN24 integration:
Use FLOW in the afternoon window (7-8 hours after the initial light exposure)
This stabilises:
- Energy dip
- Cognitive drift
- Dopamine regulation
FLOW acts as a bridge between wake and recovery
13. Nap short, not long
If you are unsafe or non-functional, nap for 20-30 minutes. Avoid long daytime naps because they reduce sleep pressure for the first local night [2].
14. Protect the first local night
Dim lights in the evening, avoid late caffeine, avoid alcohol, keep the room cool and give yourself a full sleep opportunity. The first night is not just recovery. It is a circadian instruction.
The body expects DLMO (Dim light Melatonin Onset) around 14 hours after we biologically wake to light. This is the rhythm the body follows, so it’s anticipating sunset and a reduction in light here. Support it.
HMN24 integration:
Use PRE-SLEEP 30–60 minutes before bed
This is not just sleep support:
It is a circadian instruction reinforcement
- Lowers cortisol
- Promotes parasympathetic shift
- Improves sleep architecture
After you return
15. Do not confuse “back at work” with “fully recovered”
The 2025 Oura study suggests sleep duration may bounce back quickly, while timing and architecture can remain abnormal for much longer [1].
Practical implication: the week after repeated long-haul travel should not be treated as biologically neutral. If performance matters, protect sleep consistency, morning light and evening wind-down during the return week.
HMN24 integration:
HMN24 supports circadian amplitude by reinforcing clear physiological contrast across the 24-hour cycle, not by overstimulating, but by stabilising and guiding state transitions.
In the morning, RISE establishes a strong, clean daytime signal through controlled activation and cellular support. In the afternoon, FLOW prevents the typical drop in cognitive and neurological output without relying on excessive stimulants; and in the evening, PRE-SLEEP facilitates a decisive shift into parasympathetic dominance, allowing sleep pressure and recovery processes to fully express.
The result being a stronger peak, a cleaner decline, and a deeper night phase, enhancing the amplitude of the circadian rhythm and improving overall regulation, sleep quality, and daytime performance.
Applied Travel Execution: What This Actually Looks Like in Practice
The protocol above outlines the principles.
This is what execution looks like in the real world, where timing, environment and behaviour are controlled deliberately.
1. At the Airport and Pre-Boarding
- Compression socks (15–20 mmHg, graduated) worn before boarding and throughout the flight
- 32oz water + HMN24 HYDRATE pre-flight, second serving prepared for onboard use
- Set your watch to the destination time on boarding, not on landing. Wear two watches if need be.
- Begin behavioural alignment immediately (light, caffeine, food timing)
This is where most people get it wrong; the flight does not start at take-off. It starts at the airport. In the cases of phase shifting it starts days before.
2. In-Flight Environment Control
- Light control: AYO glasses for morning anchor, eye mask for night phase
- Noise control: noise-cancelling headphones to reduce auditory stress
- Movement: every 60–90 minutes (or 30–60 if awake throughout)
- Hydration: steady intake + HYDRATE (deficit prevention, not excess intake)
- Eye care: drops to manage dryness
- Sleep support:
- PRE-SLEEP when aligned to the destination night
- Progressive Muscle Relaxation for downregulation
The cabin is not a passive environment; it is something you manage just like the environments you have at home.
3. Hotel Environment Setup
Invisible Wellness in practice.
On Arrival and to some degree Pre-Arrival: Build a Controlled Sleep Environment
- Blackout room (or mask as default)
- Remove clock visibility (reduce cognitive load)
- Use haptic + backup alarms (remove uncertainty)
- Set temperature to ~19°C / 66°F before arrival
- Open windows where possible (air exchange / CO₂ control)
- Request higher floors (noise + safety for ventilation)
- Use pillow selection + personal pillowcase
- Introduce an olfactory cue (lavender spray) to create a repeatable sleep signal
- Secure environment (lock/latch > safety perception > parasympathetic shift)
Sleep quality in a hotel is rarely accidental, it’s constructed. We aren’t quite there yet with hotels supporting biology, but in the next decade, we will be.
Travel Kit (Non-Negotiables)
Hand luggage
- HMN24 Travel Pack
- AYO Glasses
- Eye mask
- Eye drops
- Compression socks (15–20 mmHg)
- Large water bottle (32oz+)
- Noise-cancelling headphones
- Neck pillow
- L-theanine (to stabilise caffeine)
Hold luggage
- Pillow spray
- Personal pillowcase
- If you can, vacuum-pack your own pillow (they shrink) and have the hotel do it for you on your return leg.
None of these interventions solves jet lag in isolation. Together, they reduce the number of problems your circadian system has to solve.
What better cabins can and cannot solve
Modern long-range private aircraft can reduce, and many are designed to reduce, some cabin stressors.
Some premium business jets advertise lower cabin altitudes, rapid air refresh, quieter cabins, large windows and circadian lighting systems. For example, Gulfstream lists the G700 cabin altitude as 866 m at 12,497 m cruise altitude, with 100% fresh air replenished every two to three minutes; Bombardier describes its Soleil system on the Global 7500 as circadian rhythm-based cabin lighting; and Dassault describes the Falcon 8X as having a 3,900 ft cabin altitude at 41,000 ft cruise and a very quiet cabin [11-13].
All of which, if engineered and delivered correctly, can support biology.
These features can help reduce hypoxic load, noise stress, dryness and light mistiming.
But they can't eliminate jet lag.
A better cabin can reduce travel fatigue.
It cannot reset the suprachiasmatic nucleus, the brain’s master clock.
That still needs timed light, sleep opportunity, meal timing and behavioural discipline.
The best travellers don’t try to “beat” jet lag.
They manage it like a biological operating system and mitigate its deleterious effects.
The science now shows that the part you notice first, sleep duration, can recover quickly. But the deeper systems, timing, REM, deep sleep and wake stability, may remain disrupted for days or longer.
So the next time you land and feel fine by day two, remember:
Your mood may have recovered.
Your calendar may have restarted.
But your biology is undoubtedly still catching up.
The smarter strategy is not to pretend you're immune or travel hardened.
It's to travel in a way that gives your circadian system fewer problems to solve. Travel smart.
You can’t remove the stress of travel.
But you can control how your body responds to it.
Most people try to fix jet lag after it happens.
The advantage comes from managing it before, during, and after, with timing, behaviour, and aligning physiology.
References
- Chee, M.W.L. et al. (2025) ‘Insights about travel-related sleep disruption from 1.5 million nights of data’, SLEEP, 48(7), zsaf077. doi:10.1093/sleep/zsaf077.
- Riedy, S.M. and Williams, S.G. (2025) ‘Jet Lag Disorder’, CDC Yellow Book 2026: Health Information for International Travel.
- UK Civil Aviation Authority (n.d.) ‘Physiology of flight’.
- Muhm, J.M. et al. (2007) ‘Effect of aircraft-cabin altitude on passenger discomfort’, New England Journal of Medicine, 357(1), pp. 18–27. doi:10.1056/NEJMoa062770.
- Trammer, R.A. et al. (2024) ‘Effects of moderate alcohol consumption and hypobaric hypoxia: implications for passengers’ sleep, oxygen saturation and heart rate on long-haul flights’, Thorax, 79(10), pp. 970–978. doi:10.1136/thorax-2023-220998.
- Gardiner, C. et al. (2025) ‘The effect of alcohol on subsequent sleep in healthy adults: A systematic review and meta-analysis’, Sleep Medicine Reviews, 80, 102030. doi:10.1016/j.smrv.2024.102030.
- Dawson, D. and Reid, K. (1997) ‘Fatigue, alcohol and performance impairment’, Nature, 388, p. 235. doi:10.1038/40775.
- Cho, K. et al. (2000) ‘Chronic jet lag produces cognitive deficits’, Journal of Neuroscience, 20(6), RC66. doi:10.1523/JNEUROSCI.20-06-j0005.2000.
- Van den Berg, M.J., Signal, T.L. and Gander, P.H. (2020) ‘Fatigue risk management for cabin crew: the importance of company support and sufficient rest for work-life balance - a qualitative study’, Industrial Health, 58(1), pp. 2–14. doi:10.2486/indhealth.2018-0233.
- Rupp, T.L., Wesensten, N.J., Bliese, P.D. and Balkin, T.J. (2009) ‘Banking sleep: realization of benefits during subsequent sleep restriction and recovery’, SLEEP, 32(3), pp. 311–321. doi:10.5665/sleep/32.3.311.
- Gulfstream Aerospace (n.d.) ‘G700’.
- Bombardier (n.d.) ‘Global 7500’.
- 13. Dassault Falcon (2019) ‘Falcon 8X backgrounder’.
