One side of your brain keeps watch on your first night away

Key takeaways

• On a first night in a new place, the left side of the brain stayed more alert during deep sleep and woke people faster to odd sounds, a Brown University study found, and the effect was gone by the second visit¹².
• In a small 2010 trial, earplugs and an eye mask helped volunteers reach dream sleep about 41 minutes sooner in a noisy, lit room, and they rated their sleep better⁴.
• At airplane cabin pressure, two drinks before sleep dropped volunteers’ median blood oxygen to about 85% and pushed their heart rate to about 88 beats a minute, a German Aerospace Center study found⁵⁶.
• CDC calls poor sleep the most common complaint at high altitude, and advises against alcohol and opioids as sleep aids there⁸.
• FDA has warned since 2019 that zolpidem, eszopiclone and zaleplon can cause sleepwalking and even sleep driving, sometimes after a single dose¹¹.

“In Japan they say, ‘if you change your pillow, you can’t sleep,'” Brown University researcher Yuka Sasaki said in 2016¹.

Her team tested the saying. They brought 35 young, healthy volunteers into a sleep lab twice, about a week apart, and measured their brains during sleep¹².

On the first night, a network in the left hemisphere stayed more active than its partner on the right during deep sleep¹. When the researchers played odd beeps into the right ear, which feeds the left hemisphere, people were more likely to wake and responded faster¹. On the second visit, the imbalance was gone¹.

The researchers call it a “night watch”: part of the brain stays on guard in an unfamiliar place². That’s useful if a place might be dangerous. It’s less useful in a hotel the night before a big meeting.

Jet lag gets most of the attention in travel advice, and our article on travel wellness covers its light timing and melatonin. This guide covers the rest: the first night, noisy rooms, sleep on planes, altitude, sleeping pills and jet-lag apps.

Your brain posts a guard in a new room

Sleep scientists have long known about the “first-night effect,” the poor sleep people get in a new setting³. What they didn’t know was what the brain was doing.

The Brown team, led by Masako Tamaki and Sasaki, used brain scans and recordings to look inside it¹. They found the uneven sleep in one brain network, the default-mode network, and only during deep, slow-wave sleep¹. Volunteers with the biggest left-right gap slept worse³.

Anxiety didn’t seem to explain it. Volunteers reported no unusual worry, and anxiety scores didn’t differ between visits¹³.

Some birds and marine mammals sleep with one half of the brain at a time¹³. Certain birds even take the risky outer edge of a flock, letting the waking half of the brain scan for danger³. Human brains seem to do a milder, more local version².

The study had limits. It was small, the volunteers were young, and the team measured only the first stretch of deep sleep, so it’s unknown whether the watch switches sides later in the night¹.

What it means for you: expect a lighter first night, and don’t read it as a sign that something is wrong. Sleep usually improves a lot on the second night, the researchers wrote³.

Earplugs and an eye mask: a cheap test with real results

Hotel rooms bring hallway voices, ice machines, street noise and light around the curtains. The brain’s night watch listens for exactly that kind of unfamiliar signal².

The best test of earplugs and eye masks comes from an unlikely place: a simulated hospital intensive care unit. In a 2010 study in the journal Critical Care, researchers had 14 healthy adults sleep in a lab with recorded ICU noise of about 66 decibels and the lights at 100 lux⁴.

On one night they slept with earplugs and an eye mask, and on another without them⁴. With both:

• dream (REM) sleep made up about 13% of the night, compared with about 9% without them;
• REM sleep started about 41 minutes sooner;
• they woke briefly less often;
• their bodies made more melatonin, the hormone that signals night;
• they rated their sleep as better⁴.

Total sleep time and sleep efficiency didn’t change by a statistically clear amount⁴. The study was small, lasted one night and used healthy volunteers in a lab, not travelers⁴. Still, earplugs and a mask cost a few dollars and carry little risk.

CDC’s 2026 travel guide, the Yellow Book, also says an eye mask and earplugs may help you sleep on a flight¹⁰. Our upcoming articles on bedroom darkness and noise cover these tools at home.

Before relying on earplugs in a hotel, test them with your phone alarm at home so you know you’ll still wake up.

On a plane, skip the nightcap

Airplane cabins are pressurized to the equivalent of about 8,000 feet⁵⁷. Researchers at the German Aerospace Center, known as DLR, wondered what happens when you add a drink and then fall asleep.

In a study published in Thorax in 2024, healthy adults aged 18 to 40 slept for four hours on two nights, once after drinking alcohol and once sober⁵⁶. The dose was modest: about two cans of beer or two glasses of wine⁶. Seventeen people slept in an altitude chamber set to cabin pressure, and 23 slept at normal pressure⁵. DLR’s announcement says 48 people took part; the journal paper reports results for these 40⁵⁶.

What happened during sleep⁵:

Condition	Median blood oxygen	Time below 90% oxygen	Median heart rate
Normal pressure, sober	95.9%	None	64 beats a minute
Normal pressure, alcohol	95.0%	None	77 beats a minute
Cabin pressure, sober	88.1%	About 173 minutes	73 beats a minute
Cabin pressure, alcohol	85.3%	About 201 minutes	88 beats a minute

Deep sleep also shrank. With alcohol at cabin pressure, volunteers got about 47 minutes of deep sleep, compared with about 68 minutes sober at normal pressure⁵.

The authors warned that more alcohol could hit harder, especially for older passengers and people with medical conditions⁶. Andrew Freeman, a cardiologist at National Jewish Health who wasn’t part of the study, told CNN it was small but a useful starting point⁷. The study was funded by DLR’s own aeronautics program, and the authors reported no competing interests⁵.

The Yellow Book’s in-flight advice fits: keep alcohol to a minimum, since it breaks up sleep, avoid caffeine and other stimulants in the hours before you plan to sleep, and skip sedatives that linger in the body¹⁰.

Making plane sleep easier

We found no trials comparing seats or neck pillows, so treat these as practical ideas. A window seat gives you a wall to lean on and keeps seatmates from waking you. Bring your mask and earplugs or noise-canceling headphones.

Time plane sleep to bedtime at your destination, and keep water handy¹⁰. Our travel wellness article covers moving your legs on long flights.

At altitude, poor sleep is the most common complaint

Ski trips and mountain treks bring a different sleep thief: thin air. Sleep trouble is the most common complaint of travelers at high altitude, according to the CDC’s 2026 Yellow Book chapter by Peter Hackett and David Shlim⁸.

Above about 9,000 feet, nearly everyone develops periodic breathing, an uneven breathing pattern during sleep that can break it up⁸. Blood oxygen also drops most during sleep⁸. Sleep usually, though not always, gets better as you adjust⁸.

The CDC’s advice for sleeping at altitude:

• Give yourself more than one day to get from low ground to a bed at 9,000 feet or higher⁸.
• Above about 9,800 feet (3,000 meters), raise your sleeping elevation by no more than about 1,600 feet (500 meters) a day, with an extra rest day for each 3,300 feet⁸.
• Skip alcohol and opioids as sleep aids, because they slow breathing⁸. The 2024 edition advised avoiding alcohol for the first 48 hours at elevation⁹.
• Ask a clinician about acetazolamide, a prescription drug that reduces periodic breathing and raises oxygen at night⁸. The 2024 edition says travelers with obstructive sleep apnea should receive it⁹.
• If you need a sleeping pill, short-acting zolpidem or zaleplon at 5 mg is generally acceptable, with at least 8 hours before anything that needs alertness⁸.

Sleeping pills on the road: read the boxed warning

Some travelers pack a prescription sleeping pill for the trip. The Yellow Book lists hypnotics such as zolpidem and eszopiclone as options for jet lag disorder, citing American Academy of Sleep Medicine guidelines¹⁰. It also lists their downsides, including memory gaps and a higher risk of sleepwalking-type behaviors, and notes a lower starting dose of zolpidem for women¹⁰.

In April 2019, the Food and Drug Administration added a boxed warning to three of these drugs: eszopiclone (Lunesta), zaleplon (Sonata) and zolpidem (Ambien and others)¹¹. The drugs can lead people to walk, drive or do other things while not fully awake, usually with no memory of it afterward¹¹. FDA calls a boxed warning its most prominent kind¹¹.

FDA found 66 cases over 26 years that ended in serious injury or death, including 20 deaths¹¹. Some happened at the lowest recommended dose, without alcohol, or after just one pill¹¹.

That matters more in a strange room, where the door, stairs and balcony aren’t where your body expects them. FDA’s advice for these drugs:

• Take most of them right before bed and stay in bed for 7 to 8 hours; Sonata and Intermezzo need at least 4¹¹.
• Don’t mix them with alcohol, other sleep medicines, including over-the-counter ones, or other sedating drugs¹¹.
• Stop and call your prescriber if you do anything while not fully awake¹¹.
• Remember that any insomnia medicine can impair driving the next morning, even if you feel alert¹¹.

The Yellow Book adds that antihistamine sleep aids and long-acting sedatives are worth avoiding for jet lag, because they can cloud thinking and raise the risk of falls¹⁰. Our advice: never try a sleeping pill for the first time on a trip. Test it at home with a clinician’s guidance, and skip it on any flight shorter than the time you’d need to stay in bed.

Jet-lag apps rest on real science, but they haven’t been tested head to head

Westward trips feel easier than eastward ones, partly because the body clock’s natural cycle runs a little longer than 24 hours¹⁰. That’s the kind of detail jet-lag apps build in.

The Yellow Book suggests a “jet lag calculator” to time light, sleep, caffeine and melatonin to your trip¹⁰. Those tools are often based on phase-response curves, which map how light at different hours shifts the clock¹⁰. But the chapter cites no study showing that calculators reduce jet lag¹⁰.

Timeshifter, one popular app, says its chief scientist and co-founder is circadian researcher Steven Lockley, who has spent more than 20 years on the Harvard Medical School faculty¹². The company claims that in 129,852 post-trip surveys, users who followed its plans were 14.1 times less likely to report very severe jet lag¹². Those are self-reported answers from the company’s own users, not a controlled trial¹². The first plan is free, then $9.99 a plan or $24.99 a year¹².

Our take: an app can make good advice easier to follow. In our searches we found no published randomized trial showing any jet-lag app works better than following the free light-timing advice in our travel wellness article. Apply the same skepticism you’d bring to a supplement maker’s survey.

Your travel sleep kit and first-night routine

Most of what helps travel sleep is low-tech and cheap. That fits a natural-health view of the body: the night watch is a protective reflex, not a flaw, so the goal is to make a strange room feel safe and familiar.

The first-night routine

1. Book smart. If you can, schedule the big event for day two, not the morning after you arrive.
2. Ask for a quiet room. Away from elevators, ice machines and the street is a reasonable request, though no study has tested it.
3. Walk the room before bed. Find the bathroom, the door and the exit route while the lights are on, so you aren’t searching in the dark at 3 a.m.
4. Seal the light. Close and clip the curtains, cover blinking device lights, and keep the eye mask handy.
5. Bring home’s wind-down. Keep the same steps you use at home, at the same clock time if you’re in your home time zone.
6. Skip the nightcap. Alcohol fragments sleep¹⁰, and at altitude it slows breathing⁸.
7. Expect a lighter night. Waking more than usual on night one is normal. Night two is usually better³.

What the evidence shows

Claim or tool	What studies found	Evidence level
The first-night “night watch”	One hemisphere stayed more alert on night one in a 35-person lab study12	Promising but early
Earplugs and eye mask in noisy, lit rooms	Earlier REM, fewer brief wakings and better-rated sleep in 14 people4	Promising but early
Alcohol before sleeping on a long flight	Lower blood oxygen, faster heart rate and less deep sleep at cabin pressure5	Promising but early that it causes harm; small study
Alcohol or opioids as sleep aids at altitude	CDC advises against both because they slow breathing, at a time when blood oxygen already dips most during sleep8	Evidence says no, or unsafe
A Z-drug with alcohol, or without 7 to 8 hours to stay in bed	FDA warns against both; sleepwalking-type behaviors have caused injuries and deaths11	Evidence says no, or unsafe
Jet-lag apps over free guidance	Company surveys only; no controlled trial found1012	Not enough evidence

Questions readers ask

The bottom line

Travel sleep isn’t only about jet lag. Your brain keeps partial watch in a new room, cabin pressure and alcohol make a poor pair, and thin mountain air breaks up sleep for nearly everyone.

The best tools are simple: earplugs, an eye mask, a familiar routine, no nightcap and a patient first night. Treat sleeping pills with respect, try them at home first, and save your money on jet-lag apps unless one helps you follow the free advice.

Related reading

• Travel wellness starts with the basics, not a suitcase of supplements
• One in seven workers clocks in during off-hours, and sleep is the first thing to anchor
• Wellness apps help a little if you keep using them, and most people don’t
• Sleep trackers count your hours well, but their sleep stages are rough guesses

Sources

1. Brown University. “Asleep somewhere new, one brain hemisphere keeps watch” (news release on Tamaki M, Bang JW, Watanabe T, Sasaki Y, Current Biology, 2016). April 21, 2016. brown.edu
2. Tamaki M, Bang JW, Watanabe T, Sasaki Y. “Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans.” Current Biology, 2016;26:1190–1194 (NSF public access copy). par.nsf.gov
3. Tamaki M, Sasaki Y. “Trouble sleeping in a new place? Here’s why, say scientists.” The Conversation, republished by the World Economic Forum, April 25, 2016. weforum.org
4. Hu RF, Jiang XY, Zeng YM, Chen XY, Zhang YH. “Effects of earplugs and eye masks on nocturnal sleep, melatonin and cortisol in a simulated intensive care unit environment.” Critical Care, 2010;14(2):R66. pmc.ncbi.nlm.nih.gov
5. Trammer RA, Rooney D, Benderoth S, Wittkowski M, Wenzel J, Elmenhorst EM. “Effects of moderate alcohol consumption and hypobaric hypoxia: implications for passengers’ sleep, oxygen saturation and heart rate on long-haul flights.” Thorax, 2024;79(10):970. pubmed.ncbi.nlm.nih.gov
6. German Aerospace Center (DLR). “Study shows drinking alcohol on long-haul flights could affect the health of sleeping passengers.” June 6, 2024. dlr.de
7. Holcombe M. “Don’t drink before your nap on the plane. It could hurt you now and later.” CNN, via ABC17 News, June 3, 2024. abc17news.com
8. Hackett PH, Shlim DR. “High-Altitude Travel and Altitude Illness.” CDC Yellow Book 2026. CDC, April 23, 2025. cdc.gov
9. Centers for Disease Control and Prevention. “High Elevation Travel & Altitude Illness.” CDC Yellow Book 2024.
10. Riedy SM, Williams SG. “Jet Lag Disorder.” CDC Yellow Book 2026. CDC, April 23, 2025; updated July 21, 2026. cdc.gov
11. U.S. Food and Drug Administration. “FDA adds Boxed Warning for risk of serious injuries caused by sleepwalking with certain prescription insomnia medicines.” Drug Safety Communication, April 30, 2019.
12. Timeshifter. “Jet lag is history” (company product page; cited only for the company’s own claims). Accessed October 2026. timeshifter.com
13. National Heart, Lung, and Blood Institute. “Insomnia: Diagnosis.” NIH, accessed October 2026. nhlbi.nih.gov