Coronavirus (COVID-19)

COVID-19 Vaccines Please click here for information about COVID-19 vaccines. Mercyhealth Visitor Guidelines Visitor guidelines have changed at some Mercyhealth locations. Please click here... continue reading

Health Library

Return to Index


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


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

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

There are no major, lasting problems with this procedure.

What to Expect

Prior to Test

Before the test:
  • Wash your hair without any sprays, oils, or conditioners.
  • Eat a normal dinner the night of the test.
  • Don't drink alcohol or caffeine, or take any sleeping aids before the test.
  • Bring any medicines you are taking. Your doctor may ask you to stop some medicines 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. But, you may be asked to try to sleep in a certain position for part of the night. You will be watched by video during the night. This will be done in case sensors come loose. They can also be taken off so you can use the bathroom if you need to. Sometimes, it is clear during the test that you can benefit from an intervention, such as continuous positive airway pressure (CPAP). This 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 2 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

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

How Long Will It Take?

About 10-12 hours

Will It Hurt?



Results from this test may be ready right away. If not, then they are most often available within 2 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

There should not be side effects or lasting problems from the study. Call your doctor if you have any concerns.
If you think you have an emergency, call for emergency medical services right away.


American Academy of Sleep Medicine
National Sleep Foundation


Better Sleep Council Canada
Canadian Sleep Society


Polysomnography. EBSCO DynaMed Plus website. Available at: . Updated April 10, 2017. Accessed August 22, 2018.
Sleep studies. Boston Children’s Hospital website. Available at: Accessed August 22, 2018.
Sleep studies. National Heart, Lung, and Blood Institute website. Available at: Accessed August 22, 2018.
Sleep studies: In the sleep laboratory and in the home. American Thoracic Society website. Available at: Updated 2015. Accessed August 22, 2018.

Revision Information

  • Reviewer: EBSCO Medical Review Board Marcin Chwistek, MD
  • Review Date: 05/2018
  • Update Date: 08/22/2018
Mercyhealth MyChart Sign In