A Multiple Sleep Latency Test (MSLT) also known as a "Nap Study" is a daytime sleep study used to document the severity of your daytime sleepiness or chronic fatigue. It is typically performed the day following an overnight diagnostic study.

The MSLT is used to evaluate individuals who are thought to have narcolepsy or a circadian rhythm disorder. A MLST may also be used  by your physician to distinguish physical fatigue from true excessive daytime sleepiness (EDS).

Fewer sensors are required to record your physiological activity during the MSLT than during the overnight portion. However, your brain activity, eye movements, muscle tone, oxygen levels and heart rate will continue to be monitored throughout the various naps.

The study consists of five 20-minute naps scheduled 2 hours apart, the first of which is started two hours after you wake up from your overnight sleep study.

For each nap, you are asked to lie quietly in bed and try to go to sleep. Then the lights are turned off. Once the lights are out, the study will measure how long it takes you to fall asleep. During these naps your technician will monitor your sleep/wake patterns from a separate room. The MSLT lasts all day and is usually completed by late afternoon or early evening.

Once you are scheduled for an MSLT, a helpful packet of information will be sent to you that will answer any additional questions you may have and inform you on what to bring and what to expect.