Disrupted sleep-wake cycle
Narcolepsy is a rare neurological condition that affects the brain's ability to regulate the normal sleep-wake cycle. Narcolepsy is estimated to affect about 1 person in 2,500. That means that in the UK there are approximately 30,000 people who have narcolepsy, though it is believed that the majority have not been diagnosed.
Normal sleep takes the form of a regular pattern of REM (Rapid Eye Movement) and non-REM stages. During a fully night's sleep, every 90 minutes or so a normal sleeper experiences several minutes of REM sleep, during which dreaming occurs, before switching back to non-REM sleep.
Fragmented night-time sleep
In people with narcolepsy, however, the nocturnal sleep pattern is much more fragmented and typically involves numerous awakenings. When falling asleep at night, or during the day, people with narcolepsy may rapidly enter REM sleep, leading to unusual dream-like phenomena such as hallucinations.
Daytime sleepiness and cataplexy
The most common symptom of narcolepsy is excessive daytime sleepiness (EDS), brought about by an irresistible need to sleep at inappropriate times throughout the day. Many people with narcolepsy also experience cataplexy, a temporary involuntary loss of muscle control, usually in response to strong emotions.
It is usually the onset of EDS that is the first sign that a person has narcolepsy. However, there are other conditions that can cause EDS and it is important that medical advice is obtained as soon as possible (see Seeking medical help).