The earliest symptom of narcolepsy is usually daytime sleepiness, which may be extreme. However, it may take years to recognize the disorder because other, more common causes of daytime sleepiness often are blamed for the symptoms.
Narcolepsy has four main symptoms. It is common for people with narcolepsy to have more than one symptom, but it is rare for a person with the disease to experience all four:
Excessive daytime sleepiness — This is always present and is usually the most prominent symptom.
Cataplexy — This is the sudden, temporary loss of muscle tone, which causes paralysis of the head or body while the person remains conscious. It can last a few seconds or several minutes. Mild attacks can cause slurred or stuttering speech, drooping eyelids or hand weakness that causes the person to drop objects. Severe attacks can cause the knees to buckle, leading to collapse. Typically, cataplexy is brought on by laughter, excitement or anger. The sudden relaxing of muscle tone is probably the result of the brain abruptly entering REM sleep.
Sleep paralysis — This is the temporary inability to move while falling asleep or awakening. It lasts no more than several minutes. Like cataplexy, sleep paralysis probably is related to insufficient separation between REM sleep and the awake state.
Hypnagogic hallucinations — These are dreamlike images that are seen during the awake state instead of during sleep. These often-frightening visions are seen just as the person is falling asleep or waking up. They tend to occur in people who also have sleep paralysis.
Symptoms usually begin during adolescence or young adulthood. People with narcolepsy complain of fatigue, experience impaired performance at work and school, and may have difficulty in social relationships. Excessive daytime sleepiness can be disabling and may greatly diminish a person's quality of life. Memory lapses and visual disturbances may be particularly upsetting.
More than 50% of people with narcolepsy experience periods of memory lapse or blackouts caused by very short periods of sleep called micro-sleeps. Micro-sleeps are not unique to people with narcolepsy, and they can be experienced by anyone who is severely sleep deprived. They are periods of sleep that last only a few seconds, and usually are not noticed. During such episodes, a person may get lost while walking or driving, write or speak nonsense, misplace objects, or bump into things. Later in the course of narcolepsy, a person also can develop insomnia (difficulty sleeping) during normal sleeping hours.