Sleep attack! Uninvited and unwelcome, this assault demands the full attention of the body, making it impossible for a person to continue with activities.

Paul Tringali, of Oceanside, N.Y., was just 20 years old when he experienced his first sleep attack. He found himself becoming suddenly drowsy during the daytime, spells that would interfere with his college studies unless he regularly took a brief nap.

It wasn't until he was 35 that he learned that his extreme daytime drowsiness was a common symptom of narcolepsy--and that it could be dangerous. He was driving when an attack hit him and he wrecked his car. Although he was not seriously injured, Tringali realized that he needed help.

Narcolepsy is a condition that has long baffled scientists. Charlotte McCutchen, the physician in charge of sleep and circadian neuroscience at the National Institute for Neurologic Disease and Stroke in Bethesda, part of the National Institutes of Health, defines it as a disorder of sleep regulation that originates in the brain and appears to have a genetic component. But in recent months, researchers have found a tantalizing clue about its cause and a new medication has come on the market.

Now researchers are homing in on the problem. Two animal studies published this month in the journal Cell indicate that a genetic problem deep in the brain may interfere with the sleep signals between the cells of the hypothalamus, which helps regulate a number of the body's functions. These results suggest a mechanism for the disorder and may point the way to improved medications.

Meanwhile, a new prescription drug treatment called modafinil was introduced earlier this year--the first medication in more than 40 years manufactured specifically for the symptoms of narcolepsy.

One out of every 2,000 Americans is affected by this chronic problem, according to the National Sleep Foundation, a nonprofit group that promotes research on sleep disorders. Many people remain untreated. The symptoms often begin in the teens or early adulthood. But, according to the National Commission on Sleep Disorders Research, it takes about 15 years for a person with the disease to be diagnosed.

The most common symptoms of narcolepsy include:

* Excessive daytime sleepiness, sudden and irresistible "sleep attacks" that can last from a few seconds to more than an hour. These can occur any time, even while in the middle of a conversation or activity.

* Cataplexy, a sudden and debilitating loss of muscle tone that can cause a person to fall or collapse during waking hours in response to any kind of sudden emotional stimuli, such as laughter, anger or surprise. Cataplexy, found in 80 percent of narcoleptics, can make social situations quite awkward.

"The patient with this symptom may fall face forward into his soup," McCutcheon said. "This is something over which he has little control. Cataplexy is very disabling and very embarrassing."

Equally disconcerting is the threat many narcoleptics live with of having a cataplectic attack in a dangerous situation, such as driving, crossing the street or swimming.

* Hypnagogic hallucinations, which are extremely vivid--and often frightening--dreamlike visions that usually occur at the onset of sleep. They can be just as disturbing and complex as dreams.

Many patients, prior to diagnosis, assume that they are "going crazy," according to Marguerite Jones Utley, a member of the board of trustees of the support group Narcolepsy Network and author of a book on narcolepsy.

* Sleep paralysis, a symptom similar to cataplexy, which involves a temporary loss of muscle tone and the inability to move. Unlike cataplexy, which occurs when the person is conscious, sleep paralysis happens as the person is beginning to awaken from sleep.

* Disrupted nocturnal sleep. While patients with narcolepsy may fall asleep easily, staying asleep becomes difficult. Sleep that is frequently disrupted is less restful.

For diagnosis, patients usually have an overnight test at a sleep center in which they are hooked up to an electroencephalograph (EEG) that records their brain waves. Breathing, leg movements and heartbeat are also monitored. This test can help rule out other sleep disorders, particularly sleep apnea, which is a temporary cessation of breathing that disrupts sleep and also can cause daytime drowsiness.

People suspected of having narcolepsy often undergo a multiple sleep latency test (MSLT), in which the patient is hooked up to the EEG during daytime hours to see how easily he falls asleep. The patient is asked to remain awake, but every two hours is asked to take a 20-minute nap. The test consists of five of these nap periods.

The test is used to measure the ease with which the patient can fall asleep. Healthy, well-rested individuals normally take longer than 10 minutes to fall asleep, according to information from the Narcolepsy Network, a nonprofit educational and patient support organization. People with narcolepsy will generally fall asleep faster.

McCutcheon said that although there are no cures for narcolepsy, medication and lifestyle changes often can manage the symptoms. Patients are told to reduce the stress in their lives, avoid caffeine, nicotine and alcohol in the late afternoon or evening, get regular exercise and relaxation and adhere to a strict sleep/wake schedule that provides about eight hours of sleep each night.

Medications are also prescribed. Until recently, cases of excessive sleepiness were treated with stimulants such as amphetamines. But these drugs can be addictive and have unwanted side effects, such as anxiety.

Today, patients have the new drug modafinil, sold as Provigil, which has fewer side effects than the other stimulants and is longer lasting. So far, McCutchen said, the drug appears to be "quite effective and there is less in the way of cardiovascular side effects." But she cautioned that "it is not a miracle drug. Like any other drug, there are going to be people for whom it's not effective."

People who suffer from cataplexy, sleep paralysis and hypnagogic hallucinations often are treated with antidepressants. Clinical trials are underway on another drug, gamma hydroxybutyrate (GHB), to treat these problems. This substance was once available as a dietary supplement but because it was abused as a date rape drug, it was banned in 1991.

But narcolepsy experts argue that since there are so few good options for patients, the earlier reported abuse of GHB-like substances shouldn't hold back study of this drug.

"The potential benefits to a carefully selected group of patients categorically outweigh the risks," said Helene A. Emsellem, a physician and medical director for the Sleep and Wake Disorders Center, in Chevy Chase. "More research needs to be done."

Resources

* The Narcolepsy Network: 973-276-0115 or on the Web at www.websciences.org/narnet. Written materials about narcolepsy can be ordered at 1-888-412-9253.

* The National Sleep Foundation: 1522 K Street NW, Suite 510, Washington, DC 20005; or on the Web at www.sleepfoundation.org.