A multiple sleep latency test (MSLT) is a sleep study that is performed during the day to measure how sleepy you get or to discern whether breathing treatments for your disorder are working properly. An MSLT's must follow a polysomnogram and record whether you fall asleep during the test, and if so, which stages of sleep you enter. In an MSLT you are generally given five 20-minute nap opportunities spaced 2 hours apart, while a sleep technician monitors your brain activity and eye movements. An MSLT is often used to test for narcolepsy.