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What are the symptoms ?

People with narcolepsy experience highly individualized patterns of REM sleep disturbances that tend to begin subtly and may change dramatically over time. The most common major symptom, other than excessive daytime sleepiness (EDS), is cataplexy, which occurs in about 70 percent of all patients. Sleep paralysis and hallucinations are somewhat less common. Only 10 to 25 percent of patients, however, display all four of these major symptoms during the course of their illness.

Excessive daytime sleepiness
EDS, the symptom most consistently experienced by almost all patients, is usually the first to become clinically apparent. Generally, EDS interferes with normal activities on a daily basis, whether or not patients have sufficient sleep at night. People with EDS describe it as a persistent sense of mental cloudiness, a lack of energy, a depressed mood, or extreme exhaustion. Many find that they have great difficulty maintaining their concentration while at school or work. Some experience memory lapses. Many find it nearly impossible to stay alert in passive situations, as when listening to lectures or watching television. People tend to awaken from such unavoidable sleeps feeling refreshed and finding that their feelings of drowsiness and fatigue subside for an hour or two.
Involuntary sleep episodes are sometimes very brief, lasting no more than seconds at a time. As many as 40 percent of all people with narcolepsy are prone to automatic behavior during such "microsleeps." They fall asleep for a few seconds while performing a task but continue carrying it through to completion without any apparent interruption. During these episodes, people are usually engaged in habitual, essentially "second nature" activities such as taking notes in class, typing, or driving. They cannot recall their actions, and their performance is almost always impaired during a microsleep. Their handwriting may, for example, degenerate into an illegible scrawl, or they may store items in bizarre locations and then forget where they placed them. If an episode occurs while driving, patients may get lost or have an accident.

Cataplexy
Cataplexy is a sudden loss of muscle tone that leads to feelings of weakness and a loss of voluntary muscle control. Attacks can occur at any time during the waking period, with patients usually experiencing their first episodes several weeks or months after the onset of EDS. But in about 10 percent of all cases, cataplexy is the first symptom to appear and can be misdiagnosed as a manifestation of a seizure disorder. Cataplectic attacks vary in duration and severity. The loss of muscle tone can be barely perceptible, involving no more than a momentary sense of slight weakness in a limited number of muscles, such as mild drooping of the eyelids. The most severe attacks result in a complete loss of tone in all voluntary muscles, leading to total physical collapse in which patients are unable to move, speak, or keep their eyes open. But even during the most severe episodes, people remain fully conscious, a characteristic that distinguishes cataplexy from seizure disorders. Although cataplexy can occur spontaneously, it is more often triggered by sudden, strong emotions such as fear, anger, stress, excitement, or humor. Laughter is reportedly the most frequent trigger.
The loss of muscle tone during a cataplectic episode resembles the interruption of muscle activity that naturally occurs during REM sleep. A group of neurons in the brainstem ceases activity during REM sleep, inhibiting muscle movement. Using an animal model, scientists have recently learned that this same group of neurons becomes inactive during cataplectic attacks, a discovery that provides a clue to at least one of the neurological abnormalities contributing to human narcoleptic symptoms.

Sleep paralysis
The temporary inability to move or speak while falling asleep or waking up also parallels REM-induced inhibitions of voluntary muscle activity. This natural inhibition usually goes unnoticed by people who experience normal sleep because it occurs only when they are fully asleep and entering the REM stage at the appropriate time in the sleep cycle. Experiencing sleep paralysis resembles undergoing a cataplectic attack affecting the entire body. As with cataplexy, people remain fully conscious. Cataplexy and sleep paralysis are frightening events, especially when first experienced. Shocked by suddenly being unable to move, many patients fear that they may be permanently paralyzed or even dying. However, even when severe, cataplexy and sleep paralysis do not result in permanent dysfunction. After episodes end, people rapidly recover their full capacity to move and speak.

Hallucinations
Hallucinations can accompany sleep paralysis or can occur in isolation when people are falling asleep or waking up. Referred to as hypnagogic hallucinations when accompanying sleep onset and as hypnopompic hallucinations when occurring during awakening, these delusional experiences are unusually vivid and frequently frightening. Most often, the content is primarily visual, but any of the other senses can be involved. These hallucinations represent another intrusion of an element of REM sleep-dreaming-into the wakeful state.

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