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(Polysomnogram; Overnight Sleep Study; Rapid Eye Movement Studies)

Pronounced: Pol-ee-som-NAH-grah-fee


Polysomnography (PSG) is a study of sleep cycles and sleep behavior. It is usually done in a sleep center overnight. This study involves observing a person at sleep while charting brain waves and other bodily functions.

Reasons for Test    TOP

This study can evaluate sleeping problems, such as:

  • Trouble falling or staying asleep—insomnia
  • Breathing that stops during sleep—apnea
  • A problem with falling asleep suddenly during the day—narcolepsy
  • Nightmares and sleepwalking
  • Problems with arm or leg movement during sleep

Possible Complications    TOP

There are no major complications associated with this procedure.

What to Expect    TOP

Prior to Test

Before the test, you may be asked to do the following:

  • Wash your hair, but do not use any sprays, oils, or conditioners.
  • Eat a normal dinner the night of the test.
  • Do not drink alcohol or caffeinated beverages or take any sleeping aids before the test.
  • Bring any medications you are taking. When making the appointment for the sleep study, ask if you should keep taking your medications in the days before the test.
  • Bring comfortable pajamas and a bathrobe to wear.

Description of Test

You will arrive in the evening. You will be given time to relax in the room where you will sleep. Electrodes will be attached to your head, legs, and chest. Other monitors are placed around your chest, near your nose and mouth, and on your finger. You will be able to read and relax again until your bedtime.

For most of the night, you will be able to move and turn during sleep. However, you may be asked to try to sleep in a certain position for part of the night. You will be observed by video during the night. This will be done in case sensors come loose or need to be removed for you to go to the bathroom. Sometimes, it is clear during the test that you can benefit from an intervention, such as continuous positive airway pressure (CPAP). This intervention may be started midway through the night.

CPAP Assistance

Sleep monitor apnea
Copyright © Nucleus Medical Media, Inc.

Your doctor may ask for an additional test for narcolepsy. The test is known as The Multiple Sleep Latency Test (MSLT). You will need to stay for part of the next day. You will be asked to nap for up to 20 minutes every two hours. The time it takes you to fall asleep and the time it takes you to go into deep sleep will be measured.

After Test    TOP

Your sensors will be removed in the morning. In most cases, you will be able to go home.

After the procedure, be sure to follow your doctor's instructions.

How Long Will It Take?    TOP

About 10-12 hours

Will It Hurt?    TOP


Results    TOP

Results from this test may be ready right away. If not, then they are most often available within two weeks. Any abnormal breathing or leg movements during sleep will be noted. Your doctor will review the results and discuss them with you.

Call Your Doctor    TOP

There should not be side effects or complications from the study. Call your doctor if you have any concerns.

In case of an emergency, call for medical help right away.


American Academy of Sleep Medicine
National Sleep Foundation


Better Sleep Council Canada


Polysomnography. Boston Children’s Hospital website. Available at:
...(Click grey area to select URL)
Accessed August 5, 2013.
Polysomnography. KU Medical Center website. Available at:
...(Click grey area to select URL)
Accessed August 5, 2013.
Last reviewed August 2013 by Rimas Lukas, MD; Michael Woods, MD
Last Updated: 5/11/2013


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