Introduction

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People with narcolepsy can be driving or walking competently but end up in a location different from the intended one.
A narcolepsy patient can be carrying on a conversation and jump from one unrelated topic to another or just trail off and stop talking altogether.
The patient may suddenly perform bizarre actions, such as putting socks in the refrigerator.
Patients may experience severe forgetfulness.
Their movements may suddenly become slow or clumsy.
In some cases, their behavior may resemble some forms of epileptic seizures.

Disturbed Sleep. Nighttime sleep is often disturbed in narcolepsy, but it is usually mild to moderate and does not account for the daytime sleepiness experienced by people with narcolepsy.

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Periodic Limb Movement Disorder. Many patients with narcolepsy experience periodic limb movement disorder, also called PLMD (formerly known as nocturnal myoclonus). In PLMD, the leg muscles involuntarily contract every 20 to 40 seconds during sleep, occasionally arousing the patient. The patient is usually unaware of the cause of the interruption.

Healthy Sleep

In sleep studies, subjects spend about one-third of their time asleep, suggesting that most people need about 8 hours of sleep each day. Individual adults differ in the amount of sleep they need to feel well rested, however. (Infants may sleep as many as 16 hours a day.)

The daily cycle of life, which includes sleeping and waking, is called a circadian (meaning "about a day") rhythm, commonly referred to as the biologic clock. Hundreds of bodily functions follow biologic clocks, but sleeping and waking comprise the most prominent circadian rhythm. The sleeping and waking cycle is approximately 24 hours. (If confined to windowless apartments, with no clocks or other time cues, sleeping and waking as their bodies dictate, humans typically live on slightly longer than 24-hour cycles.) It usually takes the following daily patterns:

Humans are designed for daytime activity and nighttime rest.
Additionally, there is a natural peak in sleepiness at mid-day, the traditional siesta time.

In addition, daily rhythms intermesh with other factors that may interfere or change individual patterns:

The fraction-of-a-second-firing of nerve cells in the brain may be faster or slower in different individuals.
The monthly menstrual cycle in women can shift the pattern.
Light signals coming through the eyes reset the circadian cycles each day, so changes in season or various exposures to light and dark can unsettle the pattern. The importance of sunlight as a cue for circadian rhythms is dramatized by the problems experienced by people who are totally blind. They commonly suffer trouble sleeping and other rhythm disruptions.

The Response in the Brain to Light Signals

The response to light signals in the brain is an important key factor in sleep:

Light signals travel to a tiny cluster of nerves in the hypothalamus in the center of the brain, the body's master clock, which is called the supra chiasmatic nucleus or SCN.