The multiple sleep latency test (MSLT) is a test that examines excessive daytime sleepiness. MSLT measures how quickly you fall asleep in a quiet environment during the day. Also known as a daytime nap study, the MSLT is the standard tool used to diagnose narcolepsy and idiopathic hypersomnia.

The MSLT is a full-day test that consists of five scheduled naps separated by two-hour breaks. During each nap trial, you will lie quietly in bed and try to go to sleep. Once the lights go off, the test will measure how long it takes for you to fall asleep. You will be awakened after sleeping 15 minutes. If you do not fall asleep within 20 minutes, the nap trial will end.