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Cataplexy is sudden and transient episode of loss of muscle tone, often triggered by emotions. It is a rare disease (prevalence of fewer than 5 per 10,000 in the community), but frequently affects people who have narcolepsy, a disorder whose principal signs are EDS (Excessive Daytime Sleepiness), sleep attacks, sleep paralysis, hypnagogic hallucinations and disturbed night-time sleep. Cataplexy is sometimes confused with epilepsy, where a series of flashes or other stimuli cause superficially similar seizures. Cataplexy can also be present as a side effect of SSRI Discontinuation Syndrome.
The term cataplexy originates from the Greek "kata", meaning down, and plexis, meaning paralysis.
Cataplexy manifests itself as muscular weakness which may range from a barely perceptible slackening of the facial muscles to the dropping of the jaw or head, weakness at the knees, or a total collapse. Usually the speech is slurred, vision is impaired (double vision, inability to focus), but hearing and awareness remain normal. These attacks are triggered by strong emotions such as exhilaration, anger, fear, surprise, orgasm, awe, embarrassment, and laughter. A person's efforts to stave off cataplectic attacks by avoiding these emotions may greatly diminish their lives, and they may become severely restricted emotionally if diagnosis and treatment is not begun as soon as possible. 
Cataplexy may be partial or complete, affecting a range of muscle groups, from those controlling facial features to (less commonly) those controlling the entire body. 
When cataplexy happens often, or cataplexy attacks make patients fall or drop things, it can have serious effects on normal activities. It can cause accidents and be embarrassing when it happens at work or with friends. For example, narcoleptics may not pick up babies because they are afraid they may drop them. 
Despite its relation to narcolepsy, in most cases, cataplexy must be treated differently and separate medication must be taken. For many years, cataplexy has been treated with tricyclic antidepressants such as imipramine, clomipramine or protriptyline. However these can have unpleasant side-effects and so have been generally replaced by newer drugs such as venlafaxine, a more recent antidepressant. Xyrem, the brand-name of the compound (sodium)gamma-Hydroxybutyrate GHB, has been shown to treat not only cataplexic attacks, but in narcoleptics, it has also been shown to significantly reduce daytime sleepiness. Monoamine oxidase inhibitors may be used to manage both cataplexy and the REM sleep-onset symptoms of sleep paralysis and hypnagogic hallucinations.
Cataplexy in severe cases can cause vital signs to be hard to detect without a continuous auditory pulse oximeter. As an anecdotal example, one Allison Burchell, a sufferer of severe Cataplexy, has been pronounced dead three times.
Cataplexy is a medical condition. People who have cataplexy will sometimes see that some of their muscles suddenly fail them. Cataplexy often affects people who have narcolepsy. Narcolepsy is a disorder. People with narcolepsy tend to suddenly fall asleep. They cannot control when they fall asleep. Cataplexy is sometimes confused with epilepsy, where a series of flashes or other stimuli cause superficially similar seizures.
The term Cataplexy originates from the Greek kata, meaning down, and plexis, meaning a stroke or seizure.