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This is a specialised sleep study that is typically done as a follow on from a sleep polysomnographic study. It is typically not done in isolation and involves spending the better part of the day in a sleep laboratory.

This is typically done as a follow on in patients with excessive sleepiness as in suspected narcolepsy or hypersomnia. This study is not typically done in a patient with excessive sleepiness related to obstructive sleep apnea syndrome.

This involves the patient being asked to relax and allow themselves to sleep. If sleep is not achieved within 15 minutes then the patient takes a break for 2 hours and the cycle is repeated 3 to 4 times. If the patient does achieve sleep within 15 minutes, then the patient is allowed to sleep for a maximum of 20 minutes and is then woken up. The cycle is then repeated 3 to 4 times. If the patient does sleep, then the sleep is watched closely to see if the patient attains REM sleep.