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.
The loss of muscle tone in cataplexy occurs because of the inability to regulate sleep and awake states — meaning that elements of each can overlap. 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.