The Night Before Your Sleep Study: What NOT to Do

What you do in the 24 hours before a sleep study directly shapes the quality of the recording. The American Academy of Sleep Medicine publishes patient-preparation guidance precisely because small habits can mask or distort the data your sleep specialist needs. This article lists the most common pre-study mistakes and what to do instead so the study captures a typical night.

This content was reviewed by Dmitriy Kolesnik, MD, Sleep Medicine Specialist at Vector Sleep Diagnostic Center in Queens, NY.

Caffeine Cutoff: Why Timing Matters More Than Quantity

Caffeine has a half-life of roughly 5 hours in healthy adults, meaning that an afternoon coffee is still pharmacologically active at bedtime. The AASM recommends avoiding caffeine after lunch on the day of a sleep study to prevent prolonged sleep onset latency, reduced deep sleep, and increased awakenings that can distort the study’s results [Source: AASM patient preparation guidance, accessed 2026-05-13].

Cutoff applies to coffee, tea, energy drinks, sodas with caffeine, pre-workout supplements, and dark chocolate. Read labels because some pain relievers and weight-loss products also contain caffeine.

Why Alcohol the Night Before Distorts Your Sleep Study

Alcohol is a sedative that can shorten sleep onset, but it fragments the second half of the night and worsens breathing events during sleep. A sleep study performed under the influence of alcohol can overestimate the severity of sleep apnea or, in some patients, mask a true diagnosis under abnormal architecture.

Avoid alcohol on the day of the study. If you regularly consume alcohol in the evening, tell the technologist on arrival so the variation from your normal routine is documented.

Naps: Why Daytime Sleep on Study Day Is Not Allowed

Most patients are asked to avoid daytime naps the day of an in-lab sleep study. A long nap reduces sleep pressure at bedtime, which can cause prolonged sleep latency in the lab and reduce the total sleep time captured. Insufficient total sleep time can make a study non-diagnostic and require repeat testing.

If you typically nap because of severe daytime sleepiness, ask your sleep physician for explicit instructions. Some studies, including the Multiple Sleep Latency Test, require a specific pattern of sleep the night before.

Hair Products and Electrode Adhesion

Polysomnography uses scalp electrodes to record brain waves. Gels, mousses, oils, dry shampoos, hair sprays, and leave-in conditioners reduce the contact between skin and electrode, increasing electrical impedance and degrading the EEG channels. Wash your hair the morning of the study with a clean rinse and let it air dry. Skip product application until after the study.

Nail Polish, Fake Nails, and Pulse Oximetry

The pulse oximeter clips onto a fingertip and measures oxygen saturation by shining red and infrared light through the nail. Dark polish, glitter, and acrylic nails on the index, middle, and ring fingers can block the signal. Remove polish on at least the index and middle finger of one hand before arrival.

Quick Reference: Night-Before Do and Don’t

Do	Don’t
Eat a normal dinner	Drink coffee, tea, soda, or energy drinks after lunch
Wash hair the morning of the study and let it air dry	Apply gel, mousse, oils, or hairspray
Take prescription medications on the normal schedule	Drink alcohol
Remove nail polish from at least two fingers	Take a long afternoon nap
Pack two-piece sleepwear	Wear one-piece pajamas or back-tie gowns

If You Forget Something, Tell the Technologist

If you drink coffee out of habit, accidentally use hair product, or take a nap, do not skip the appointment. Tell the technologist at check-in. Each variable is recorded on your study record so the interpreting physician can account for it. A documented variable is far better than an unexplained finding when the study is read.

What If You Cannot Fall Asleep at the Lab?

Most patients are surprised by how well they sleep in the lab. Familiar pillows, normal bedtime routines, and reading a book before lights out all help. If insomnia is your underlying complaint and you suspect sleeplessness will affect the study, talk to your sleep physician before the appointment about whether a structured insomnia evaluation belongs in the workup.

What If You Travel for the Study?

Patients who live more than an hour from the lab sometimes arrive late, hungry, or wired from traffic. None of those states help you fall asleep at lights out. Plan to arrive 30 minutes before the scheduled check-in, eat a normal dinner before you leave home, and bring a small bag of familiar items, such as a pillow, a book, or a phone charger. The room is yours for the night; treating it like a brief hotel stay reduces the novelty effect that keeps some people awake on the first lab night.

If you have to travel from outside Queens, give yourself a buffer for traffic and parking. The technologist needs the full sensor-placement window before lights out; arriving late reduces the time available to record sleep and may shorten an otherwise normal study.

Frequently Asked Questions

Can I drink caffeine in the morning before my sleep study?

One morning cup is usually fine. The AASM recommends cutting off caffeine after lunch on study day. If you are sensitive to caffeine, skip it entirely.

What if I accidentally drank alcohol the day of my study?

Tell the technologist on arrival. Depending on how much, your sleep physician may still interpret the study with a note, or may ask you to reschedule.

Why can’t I nap before my sleep study?

A nap reduces sleep pressure at night and can make it harder to fall asleep in the lab, shortening the recording and reducing diagnostic yield.

Can I wear makeup to my sleep study?

Light makeup is fine. Heavy foundation, oil-based products, and eye makeup interfere with the electrodes placed on your forehead and around your eyes.

Should I bring sleep aids I do not have a prescription for?

Bring them and tell the technologist. Over-the-counter sleep aids, melatonin, and antihistamines affect sleep architecture and must be noted on your record.

Ready for answers? Schedule a sleep evaluation at Vector Sleep Diagnostic Center in Queens, NY.