If your doctor suggests you undergo a sleep study, or polysomnography, you may be wondering what is involved in this test and what to expect. Sleep studies help doctors diagnose sleep disorders such as sleep apnoea, periodic limb movement disorder, narcolepsy, restless legs syndrome, insomnia, and night-time behaviours like sleepwalking and REM sleep behaviour disorder. Often these disorders cannot be identified with a normal office visit—your doctor needs to gather more conclusive evidence while you’re asleep.

A sleep study is a non-invasive, overnight exam that allows doctors to monitor you while you sleep to see what’s happening in your brain and body. For this test, you will go to a sleep lab that is set up for overnight stays—usually in a hospital or sleep centre. While you sleep, an EEG monitors your sleep stages and the cycles of REM and non-REM or NREM sleep you go through during the night, to identify possible disruptions in the pattern of your sleep. A sleep study will also measure things such as eye movements, oxygen levels in your blood (through a sensor—there are no needles involved), heart and breathing rates, snoring, and body movements.

A sleep study is done in a room that is made to be comfortable and dark for sleeping. You’ll be asked to arrive roughly two hours before bedtime. You can bring personal items related to sleep, and you can sleep in your own pajamas. Before you go to bed in the exam room, a technologist will place sensors, or electrodes, on your head and body, but you’ll still have plenty of room to move and get comfortable. Polysomnographic technologists monitor you during the night and can help you if you need to use the bathroom, for example. Many people wonder how they’ll be able to sleep under these conditions. Don’t worry about this too much—a full night of sleep is not required to gather useful information from your sleep study.

The data from your sleep study will usually be taken by a technologist, and later evaluated by your doctor. This may take up to two weeks, when you’ll schedule a follow up to discuss the results.

https://www.sleepfoundation.org/excessive-sleepiness/diagnosis/how-does-sleep-study-work

https://www.mayoclinic.org/tests-procedures/polysomnography/about/pac-20394877