Narcolepsy is a chronic neurological disorder caused by the brain's inability to regulate sleep-wake cycles normally. At
various times throughout the day, people with narcolepsy experience fleeting urges to sleep. If the urge becomes overwhelming,
patients fall asleep for periods lasting from a few seconds to several minutes. In rare cases, some people may remain asleep
for an hour or longer.
Narcoleptic sleep episodes can occur at any time, and thus frequently prove profoundly disabling. People may involuntarily
fall asleep while at work or at school, when having a conversation, playing a game, eating a meal, or, most dangerously, when
driving an automobile or operating other types of potentially hazardous machinery. In addition to daytime sleepiness, three
other major symptoms frequently characterize narcolepsy: cataplexy, or the sudden loss of voluntary muscle tone; vivid
hallucinations during sleep onset or upon awakening; and brief episodes of total paralysis at the beginning
or end of sleep.
Contrary to common beliefs, people with narcolepsy do not spend a substantially greater proportion of their time asleep
during a 24-hour period than do normal sleepers. In addition to daytime drowsiness and involuntary sleep episodes, most patients
also experience frequent awakenings during nighttime sleep. For these reasons, narcolepsy is considered to be a disorder of
the normal boundaries between the sleeping and waking states.
For most adults, a normal night's sleep lasts about 8 hours and is composed of four to six separate sleep cycles. A sleep
cycle is defined by a segment of non-rapid eye movement (NREM) sleep followed by a period of rapid eye movement (REM) sleep.
The NREM segment can be further divided into stages according to the size and frequency of brain waves. REM sleep, in contrast,
is accompanied by bursts of rapid eye movement (hence the acronym REM sleep) along with sharply
heightened brain activity and temporary paralysis of the muscles that control posture and body movement. When subjects are
awakened from sleep, they report that they were "having a dream" more often if they had been in REM sleep than if they had
been in NREM sleep. Transitions from NREM to REM sleep are governed by interactions among groups of neurons (nerve cells)
in certain parts of the brain.
Scientists now believe that narcolepsy results from disease processes affecting brain mechanisms that regulate REM sleep.
For normal sleepers a typical sleep cycle is about 100 - 110 minutes long, beginning with NREM sleep and transitioning to
REM sleep after 80 - 100 minutes. But, people with narcolepsy frequently enter REM sleep within a few minutes of falling asleep.