Narcolepsy is a sleep-wake control disorder in which elements of sleep intrude into wakefulness and elements of wakefulness intrude into sleep.

Excessive daytime sleepiness is when a person is so drowsy that they’re unable to stay awake during regular activities. It usually occurs as a result of sleep deprivation, such as when taking a red-eye flight or studying all night. This excessive sleepiness feels unpleasant in the moment but can be resolved by a good night’s sleep.

People with narcolepsy experience excessive daytime sleepiness that they can’t simply “sleep off”. These individuals have trouble sleeping through the night. They fall asleep quickly but their sleep is fragmented due to frequent awakenings that can worsen their daytime sleepiness. Even after a full night of sleep, an individual with narcolepsy feels as though they’ve only slept a few hours. The sleepiness is so severe that they often fall asleep throughout the day at inappropriate times, like at school or work. These episodes are commonly referred to as sleep attacks.

When people with narcolepsy do manage to stay awake, they’re typically very drowsy and experience brain fog, where they forget things and lack focus and mental clarity. In children, excessive sleepiness can cause irritability, hyperactivity, and inattentiveness.

People with narcolepsy experience dream-like hallucinations as they’re falling asleep or waking up. These hallucinations are so vivid, they seem real. They make the person feel, hear or see things that don’t exist and could be frightening. For example, hallucinations may make someone perceive that there’s a dangerous stranger or animal in the room. Hypnagogic hallucinations occur as the individual is falling asleep, while hypnopompic hallucinations occur as they awaken.

Another symptom of narcolepsy is sleep paralysis, a brief inability to move or speak while drifting off to sleep or upon waking. Sleep paralysis episodes can be frightening. The immobility may be accompanied by hallucinations, difficulty breathing, or a sensation of suffocation. Sleep paralysis can also occur occasionally in people who don’t have narcolepsy.

Laughter, joking, excitement, or, in some individuals, anger or grief, can trigger a 1-to 2-minute loss of muscle control called cataplexy in about 60% of people with narcolepsy. Cataplexy typically begins in the face, interrupting smiling or other facial expressions. It can also affect the neck, core muscles, and knees. Severe episodes can induce weakness in both legs, causing the person to collapse to the ground. People remain conscious during cataplexy, so they’re fully aware of the situation but can’t speak while it’s happening.

Individuals with narcolepsy can exhibit automatic behaviors. This happens when they continue an activity they were engaged in while they experience a brief sleep episode. The person appears awake but is actually in a state between wakefulness and sleep and isn’t aware of their actions. For example, a student in class may continue writing but is actually just scrawling lines or gibberish on the page. If this occurs while driving, individuals may get lost or have an accident. People tend to wake up from these episodes feeling refreshed, finding that their drowsiness and fatigue has temporarily subsided.

Mild obesity is common among those with narcolepsy. People may gain weight at the onset of narcolepsy; this weight gain can be dramatic in children and is sometimes accompanied by early puberty.

What Causes Narcolepsy?

Orexin-A and -B (also known as hypocretin-1 and hypocretin-2) are chemical messengers in the brain that are in charge of promoting wakefulness. Their activity during the day keep us alert and prevents us from transitioning to sleep.

In healthy people, sleep progresses through a repeated sequence of stages called the sleep cycle. It starts in lighter sleep, goes into deep sleep, and ends in a sleep stage called rapid eye movement (REM) sleep. This stage is associated with vivid dreams, rapid movement of the eyes, and temporary paralysis of the rest of the body. The REM cycle begins occurring after about an hour and a half of sleep; each stage lasts a few minutes in the first half of the night, and this duration increases during the second half of the night.

In people with narcolepsy, REM sleep often begins within minutes after falling asleep and can enter into wakefulness. This allows REM sleep-related phenomena, such as muscle weakness (cataplexy), dream-like hallucinations, and sleep paralysis, to break into waking life. Narcolepsy is caused by a loss of orexin-A and –B, impairing the brain’s ability to regulate sleep and wakefulness and disrupting the healthy sleep cycle.

What Can Cause a Loss of Orexin?

An autoimmune disease. This is a condition in which your immune system attacks your body. Some scientists think that orexin-producing neurons can be selectively killed by an autoimmune process.

It may become lost in translation. Our DNA is composed of an “alphabet” that’s used to write the “code words” for chains of molecules. Changes in the translation of the genetic code used to produce orexin could result in the loss of this chemical messenger.

Something else. In rare cases, a brain tumor that damages orexin-producing neurons can cause narcolepsy symptoms.

People with narcolepsy are typically classified as having either narcolepsy type 1 (narcolepsy with cataplexy) or narcolepsy type 2 (narcolepsy without cataplexy). Those with narcolepsy type 1 have orexin deficiency. The cause of narcolepsy type 2 is unknown.

Narcolepsy is a serious condition that can greatly impact people’s lives. Thankfully, it can be managed with the right care. Check out part two of this article, where we discuss how narcolepsy is diagnosed and treated.