Because other conditions can mimic its symptoms, in many cases narcolepsy can be difficult to diagnose. Sleep deprivation can cause excessive daytime sleepiness (EDS), and as many as a thirds of Americans do not get enough sleep. A wide range of sleep disorders can cause EDS, such as sleep apnea and insomnia. To diagnose narcolepsy, doctors often use two tests, polysomnography (PSG) and the multiple sleep latency test (MSLT). PSG is usually conducted overnight in a sleep clinic and tracks a person’s breathing, muscle movement, and brain activity. MSLT, on the other hand, is normally conducted in the morning immediately following a PSG. This test measures how quickly a person is able to fall asleep, and how quickly they can enter REM sleep.