Narcolepsy (NAR-ko-lep-se) is a disorder that causes periods of extreme daytime sleepiness. The disorder also may cause muscle weakness.
Most people who have narcolepsy have trouble sleeping at night. Some people who have the disorder fall asleep suddenly, even if they’re in the middle of talking, eating, or another activity.
Narcolepsy also can cause:
The two main phases of sleep are nonrapid eye movement (NREM) and rapid eye movement (REM). Most people are in the NREM phase when they first fall asleep. After about 90 minutes of sleep, most people go from NREM to REM sleep.
Dreaming occurs during the REM phase of sleep. During REM, your muscles normally become limp. This prevents you from acting out your dreams.
People who have narcolepsy often fall into REM sleep quickly and wake up directly from it. As a result, they may have vivid dreams while falling asleep and waking up.
Hypocretin (hi-po-KREET-in), a chemical in the brain, helps promote wakefulness. Most people who have narcolepsy have low levels of this chemical. What causes these low levels isn’t well understood.
Researchers think that certain factors may work together to cause a lack of hypocretin. These factors may include heredity, infections, brain injuries, and autoimmune disorders. (Autoimmune disorders occur if the body’s immune system mistakenly attacks the body’s cells and tissues.)
Source: National Heart, Lung, and Blood Institute, National Institutes of Health