The MSLT is used to test for central disorders of hypersomnolence such as narcolepsy or idiopathic hypersomnia, or to distinguish between physical tiredness and true excessive daytime sleepiness.
Its main purpose is to discover how readily a person will fall asleep in a conducive setting, how consistent or variable this is, and whether there are abnormalities in the rapidity of REM sleep onset.
During the test, data such as the patient's brain waves, EEG, muscle activity, and eye movements are monitored and recorded.
[5] They informally called the 0–5 minute range the twilight zone due to its indication of extreme physical and mental impairment.
[8] Preparation: On the day of the test the patient is asked not to consume any stimulants, such as tea, coffee, colas, and chocolate.