Narcolepsy

Narcolepsy's main symptom is excessive and overwhelming daytime sleepiness, even after adequate nighttime sleep. In addition, nighttime sleep may be fragmented by frequent awakenings. People who have narcolepsy often fall asleep at inappropriate times and places.

Although television sitcoms occasionally feature these individuals to generate a few laughs, narcolepsy is no laughing matter. People who have narcolepsy experience daytime "sleep attacks" that last from seconds to more than one-half hour, can occur without warning, and may cause injury. These embarrassing sleep spells can also make it difficult to work and to maintain normal personal or social relationships.

With narcolepsy, the usually sharp distinctions between being asleep and awake are blurred. Also, people who have narcolepsy tend to fall directly into dream-filled REM sleep, rather than enter REM sleep gradually after passing through the non-REM sleep stages first.

In addition to overwhelming daytime sleepiness, narcolepsy has three other commonly associated symptoms, but these may not occur in all people:

• Sudden muscle weakness (cataplexy). This weakness is similar to the paralysis that normally occurs during REM sleep, but it lasts a few seconds to minutes while an individual is awake. Cataplexy tends to be triggered by sudden emotional reactions, such as anger, surprise, fear, or laughter. The weakness may show up as limpness at the neck, buckling of the knees, or sagging facial muscles affecting speech, or it may cause a complete body collapse.
• Sleep paralysis. People who have narcolepsy may experience a temporary inability to talk or move when falling asleep or waking up, as if they were glued to their beds.
• Vivid (hypnogogic) dreams. These dreams tend to surface when people who have narcolepsy first fall asleep. The dreams are so lifelike that they can be confused with reality.

Experts estimate that as many as 350,000 Americans have narcolepsy, but fewer than 50,000 are diagnosed. The disorder is as widespread as

When you have a sleep disorder, you need to discuss your symptoms and progress so your doctor can know when it's necessary to change the course of treatment. Patient support groups are also invaluable sources of information. BOB BALKAM

Parkinson's disease or multiple sclerosis, and more prevalent than cystic fibrosis, but it is less well known. Narcolepsy is often mistaken for depression, epilepsy, or the side effects of medicines.

Narcolepsy can be difficult to diagnose in people who have only the symptom of excessive daytime sleepiness. It is usually diagnosed with the aid of an overnight sleep recording (PSG) and the MSLT.

(See "How Are Sleep Disorders Diagnosed?".) Both tests reveal signs of narcolepsy - the tendency to fall asleep rapidly and enter REM sleep early, even during brief naps.