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The chief symptom associated with narcolepsy is a consistent and overwhelming sense of daytime drowsiness that causes people to suddenly fall asleep at any point. Such drowsiness is often the first indicator that a person is developing narcolepsy. Patients may nod off regardless of their circumstances and may remain asleep for anywhere from a few minutes to an hour.

Patients typically fall asleep after a meal or after engaging in low-stimulation activities (e.g., reading, attending a classroom lecture), but sudden sleep can strike at any time. It is common for someone with narcolepsy to fall asleep while in the middle of a task or a conversation. Patients often dream during this sleep. When they awaken, they usually feel rested but are tired again within a few hours.  

People with narcolepsy often experience cataplexy, a sudden, uncontrollable loss of muscle tone that may appear similar to a seizure. Subtle symptoms of cataplexy may include slurred speech, sagging jaw and drooping eyelids. More severe symptoms may include buckling knees and even physical collapse. Episodes last for a few seconds to several minutes. Cataplexy may be triggered by intense emotions such as anger. Up to 70 percent of narcoleptic patients experience this symptom, according to the National Sleep Foundation (NSF). However, its frequency varies widely. For example, cataplexy may strike some patients several times over the course of each day, whereas other patients experience just a couple of episodes each year. Cataplexy does not involve loss of consciousness.

Sleep paralysis is a less frequent phenomenon marked by a temporary inability to speak or move. It usually occurs while the patient is falling asleep or just after the patient wakes up, and it lasts for 10 minutes or less. Patients may also feel as though they are unable to breathe during an episode of sleep paralysis.

Hypnagogic hallucinations may occur when a patient quickly falls into REM sleep. Hypnopompic hallucinations occur as the patient is awakening.  Patients in these states remain partially awake, causing them to have intense, frightening dreams that they perceive as reality. These dreams may involve a blending of dream material with elements that are actually present in the patient’s environment.

Up to 60 percent of narcoleptic patients experience sleep paralysis, hypnagogic hallucinations or both, according to the NSF. When both conditions occur together, patients have the terrifying sensation of seeing hallucinations while being unable to move or speak.

Occasionally, patients may continue to function normally during a sleep episode. However, they awaken and have no memory of their preceding activities or conversations. This automatic behavior occurs in up to 80 percent of narcoleptic patients, according to the NSF.

Restless sleep during overnight hours and visual disturbances (such as blurred vision and droopy eyelids) are other symptoms often associated with narcolepsy.

In many cases, the symptoms associated with a patient’s narcolepsy will wax and wane over time. However, symptoms rarely disappear completely. The exception is cataplexy, which may subside over time.

Patients with narcolepsy may also experience other problems associated with their condition. Lack of sleep can cause patients to become lethargic and may affect work or school performance. Lower sex drive and impotence may also result from this condition.

Sudden attacks of sleep can also present dangers if they occur at particularly undesirable times, such as when a person is driving a car or preparing food over a hot stove.