Narcolepsy is a sleep disorder that features excessive daytime sleepiness.In a tycpial sleep cycle, a person will first enter the early stage of sleep, then the deeper sleep stages. This is when REM sleep occurs. It takes around 60–90 minutes to reach the stage of REM sleep.

For people with narcolepsy, however, REM sleep occurs

There are two main types of narcolepsy: type 1 and type 2.

within 15 minutes in the sleep cycle and intermittently during the waking hours. It is during REM sleep that vivid dreams and muscle paralysis occur.Type 1 involves sleepiness and cataplexy. Tests will show that the person is almost entirely missing a neurotransmitter known as hypocretin. This may occur after an infection triggers an autoimmune condition.

Type 2 mainly involves excessive daytime sleepiness, but there is usually no sudden weakness.

Secondary narcolepsy can result when trauma or a tumor results in damage to the hypothalamus. This is a part of the brain involved in sleep.