Narcolepsy is a sleep disorder that is characterized by excessive sleepiness, sleep attacks, sleep paralysis, hallucinations and, for some, sudden loss of muscle control (cataplexy). It affects roughly 1 in 2,000 to 3,000 people but can go undiagnosed for many years

Narcolepsy is a condition which the four most common narcolepsy symptoms:

  1. Hypnagogic hallucinations are imagined sensations that seem very real as a person is falling asleep, and are also referred to as sleep hallucinations. These vivid hallucinations as they fall asleep, or just before falling asleep, can be images, smells, tastes, tactile sensations, or sounds. A person may also feel as if they are moving while their body is still. This sensation could be a feeling of falling or flying.
  2. Sleep paralysis is a feeling of being conscious but unable to move. It occurs when a person passes between stages of wakefulness and sleep. During these transitions, you may be unable to move or speak for a few seconds up to a few minutes. Some people may also feel pressure or a sense of choking.  Sleep paralysisis due to an irregularity in passing between the stages of sleep and wakefulness.
  3. Daytime sleepiness
  4. Cataplexy—a sudden loss of muscle tone and control while awake. Cataplexy is a sudden and uncontrollable muscle weakness or paralysis that comes on during the day and is often triggered by a strong emotion, such as excitement or laughter. Without much warning, the person loses muscle tone and can have a slack jaw, broken speech, buckled knees or total weakness in their face, arms, legs, and trunk. A person experiencing total cataplexy stays awake and is aware of what is happening, but cannot move. These episodes last up to a minute or two, and some people may fall asleep afterwards. The frequency of cataplexy episodes varies widely among people with narcolepsy. Some individuals avoid emotions that may bring on cataplexy.

Why does this occur? The loss of muscle tone in cataplexy occurs because of the inability to regulate sleep and awake states. During normal rapid eye movement (REM) sleep, there is a natural loss of muscle tone. In the case of cataplexy, that characteristic of REM sleep occurs suddenly during the day, causing weakness or full paralysis, even as the person remains awake during the episode.  

An interesting study recently published looked at patients with narcolepsy and their families (including second and third order relatives) and whether those families with more than one narcolepsy members suffered some of the symptoms of narcolepsy more than those patients who were the only member of the family with diagnosed narcolepsy. The role in particular of genetics, given the risk for narcolepsy has been estimated to be between 10 and 40 times higher among families with a narcoleptic member than in the general population

(S. Nevsimalova et al Sleep, 20 (1997), pp 1021-2016) 

Longitudinal study of narcolepsy symptoms in first, second, and third-degree relatives of simplex and multiplex narcolepsy families.

Assess the development and extent of narcolepsy symptoms in first-, second, and third-degree relatives and to compare multiplex (families with more than one member with narcolepsy) and simplex (families with only one member diagnosed with narcolepsy) families.

362 narcoleptic individuals were entered in the study, with a total of with 3255 family members interviewed twice, five to seven years apart. A total of 1123 family members from 72 narcolepsy patients were identified as members of multiplex families. A total of 2132 family members from 290 narcolepsy patients were identified as members of simplex families.

A control group (n = 178) composed of spouses or housemates was also interviewed twice, who did not have narcolepsy

Multiplex families had higher incidence and chronicity of hypersomnolence than the simplex family members and the control group.

Prevalence of sleep paralysis was higher among the first- and second-degree relatives coming from multiplex families, while incidence was the highest among second- and third-degree relatives. 

Hypnagogic hallucinations had similar prevalence between multiplex and simplex families but the incidence and chronicity were significantly higher among multiplex families.

Ohayon M et al Sleep Med 2018 Jul 6;53:88-93.