What Is Narcolepsy?

Narcolepsy (NAR-ko-lep-se) is a disorder that causes periods of extreme daytime sleepiness. It also may cause muscle weakness.

Rarely, people who have this disorder fall asleep suddenly, even if they're in the middle of talking, eating, or another activity. Most people who have narcolepsy also have trouble sleeping at night.

Narcolepsy also may cause:

• Cataplexy (KAT-a-plek-se). This condition causes a sudden loss of muscle tone while you're awake. Muscle weakness can occur in certain parts of your body or in your whole body. For example, if cataplexy affects your hand, you may drop what you're holding. Strong emotions often trigger this weakness. It may last seconds or minutes.
• Hallucinations (ha-lu-si-NA-shuns). These vivid dreams occur while falling asleep or waking up.
• Sleep paralysis (pah-RAL-i-sis). This condition prevents you from moving or speaking while waking up and sometimes while falling asleep. Sleep paralysis usually goes away within a few minutes.

Overview

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. (For more information on sleep cycles, see the National Heart, Lung, and Blood Institute's "Your Guide to Healthy Sleep.")

People who have narcolepsy often fall into REM sleep quickly and wake up directly from it. This is linked to vivid dreams while waking up and falling asleep.

Hypocretin, a chemical in the brain, helps control levels of 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. Examples include heredity; brain injuries; contact with toxins, such as pesticides; and autoimmune disorders. (Autoimmune disorders occur when the body's immune system attacks the body's healthy cells.)

Outlook

Narcolepsy affects between 50,000 and 2.4 million people in the United States. Symptoms usually begin during the teen or young adult years. Due to extreme tiredness, people who have narcolepsy may find it hard to function at school, work, home, and in social situations.

Narcolepsy has no cure, but medicines, lifestyle changes, and other therapies can improve symptoms. Research on the causes of narcolepsy and new ways to treat it is ongoing.

November 2008