We have all felt it. The first night in a hotel, at a friend’s house, or even moving into a new apartment, sleep just doesn’t come easily. You wake more often, toss and turn, and feel far from restored the next morning. This isn’t simply personal restlessness,it is a well-documented biological phenomenon known as the “first-night effect” (FNE).

The science behind FNE is fascinating, and understanding it can help us better manage sleep in unfamiliar settings, whether travelling for work, adjusting to new environments, or recovering between high-pressure performance days.

The Core Pattern of the First-Night Effect

Research consistently shows that on the first night in an unfamiliar environment, people experience measurable sleep disruption. Compared to subsequent nights, the first night is marked by:

• Longer time to fall asleep

• Less total sleep

• Lower sleep efficiency

• More frequent awakenings

This is so reliable that in sleep laboratories, scientists often discard the first night of data entirely to avoid skewed results (Zhang et al., 2024; Ferretti et al., 2024; Wood et al., 2023). Importantly, it isn’t just a lab artifact. The same effect shows up in hotels, hospitals, and other real-world environments (Hutchison et al., 2008).

Not everyone is affected to the same degree. People with higher baseline anxiety or those who naturally sleep lightly are more vulnerable (Rains, 2001; Zhang et al., 2024).

Why Does It Happen?

An Evolutionary Night Watch

In 2016, Tamaki and colleagues uncovered that during the first night in a new place, the brain doesn’t fully “switch off” in both hemispheres. One side of the brain remains in a lighter stage of sleep, acting almost like a sentinel, while the other enters deeper rest (Tamaki et al., 2016). This asymmetry is thought to be an evolutionary adaptation, akin to some birds and marine mammals that sleep with one eye open for safety.

Hyperarousal and Threat Detection

New sounds, smells, lighting, or even bedding trigger heightened activity in the limbic system, especially the amygdala, which is tuned for threat detection. This leads to fragmented sleep, more micro-awakenings, and less restorative deep sleep (Ferretti et al., 2024; Zhang et al., 2024).

Circadian Disruption

The circadian system, our internal clock, plays its part. Exposure to unfamiliar light at night, changes in pre-sleep routine, or shifts in meal and activity timing can all destabilise circadian cues. In travel or shift-work contexts, this mismatch between body clock and environment compounds the first-night effect (Zhang et al., 2024).

Implications Beyond the Lab

For everyday life, the FNE explains why business travellers, athletes, or anyone adjusting to a new setting often feel more fatigued on day one. For clinicians, it highlights why accurate sleep assessment requires adaptation nights. And for high performers, it reinforces that the quality of recovery is tightly linked to context, not just time in bed.

Practical Ways to Reduce the First-Night Effect

While FNE cannot be eliminated completely, it is a protective mechanism, it can be reduced:

• Environmental familiarisation: Bring elements from home such as a pillow, blanket, or familiar scent to reduce novelty (Ferretti et al., 2024).

• Light control: Minimise blue light exposure in the evening, and anchor your rhythm with bright morning light to stabilise circadian cues (Zhang et al., 2024).

• Pre-sleep rituals: Keep your bedtime routine consistent, reading, stretching, or relaxation practices signal safety to the brain.

• Gradual adaptation: If possible, arrive a day early to allow your body one “adaptation night” before a key performance day (Hutchison et al., 2008).

How This Links to Human Performance

For those who need to perform under pressure, FNE isn’t just about one bad night’s sleep , it can directly impact reaction time, mood regulation, and cognitive sharpness the following day. Managing it is therefore not only about comfort but about sustaining peak output.

This is where broader strategies matter. Nutrition, supplementation, and hydration can play supportive roles. For example:

• Supporting circadian activation: Ingredients in HMN24 RISE can help stabilise morning energy when sleep has been disrupted.

• Optimising focus under fatigue: The cholinergic and dopaminergic support in HMN24 FLOW can help maintain mental clarity after a poor night.

• Protecting recovery: HMN24 PRE-SLEEP is designed to promote deeper rest and resilience when circadian and environmental factors are stacked against you.

• Managing travel and time zone shifts: The HMN24 Travel Pack brings these tools together with hydration support for those navigating the double burden of unfamiliar environments and jet lag.

The goal is not to override biology, but to work alongside it, mitigating the cost of disruption while reinforcing the cues your brain and body rely on to adapt.

Conclusion

The first-night effect is more than a quirky observation. It reflects a deeply rooted neurobiological strategy: part of our brain literally stands guard when we sleep somewhere new. While adaptive from an evolutionary standpoint, in modern contexts it can compromise recovery when we need it most.

By understanding the science and putting the right strategies in place, from light management and routine to smart supplementation, we can soften its impact. This is precisely why we designed the HMN24 system: not to fight biology, but to align with it, even in the most demanding environments.

References

Ferretti, D., Íslind, A., Ólafsdóttir, K., Sigurðardóttir, S., Jóhannsdóttir, K., Hedner, J., … & Arnardóttir, E. (2024). Feasibility and usability of three consecutive nights with self‐applied, home polysomnography. Journal of Sleep Research, 34(2). https://doi.org/10.1111/jsr.14286

Hu, S., Shi, L., Li, Z., Ma, Y., Li, J., Bao, Y., … & Sun, H. (2023). First‐night effect in insomnia disorder: a systematic review and meta‐analysis of polysomnographic findings. Journal of Sleep Research, 33(1). https://doi.org/10.1111/jsr.13942

Hutchison, K., Song, Y., Wang, L., & Malow, B. (2008). Analysis of sleep parameters in patients with obstructive sleep apnea studied in a hospital vs. a hotel-based sleep center. Journal of Clinical Sleep Medicine, 04(02), 119-122. https://doi.org/10.5664/jcsm.27127

Rains, J. (2001). Polysomnography necessitates experimental control of the “first night effect”. Headache, 41(9), 917-918. https://doi.org/10.1111/j.1526-4610.2001.01173.x

Tamaki, M., Bang, J., Watanabe, T., & Sasaki, Y. (2016). Night watch in one brain hemisphere during sleep associated with the first-night effect in humans. Current Biology, 26(9), 1190-1194. https://doi.org/10.1016/j.cub.2016.02.063

Wood, E., Westphal, J., & Lerner, I. (2023). Re‐evaluating two popular eeg‐based mobile sleep‐monitoring devices for home use. Journal of Sleep Research, 32(5). https://doi.org/10.1111/jsr.13824

Zhang, Y., Chen, K., Xu, Y., & Wu, H. (2024). Research progress on the first‐night effect in polysomnography studies. Sleep Research, 1(1), 19-26. https://doi.org/10.1002/slp2.12