Cataplexy refers to:
Narcolepsy is both a disorder of the ability to sustain wakefulness voluntarily and a disorder of REM sleep regulation.
The classic "narcolepsy tetrad" consists of excessive day time somnolence plus three specific symptoms related to an intrusion of REM sleep characteristics (e.g., muscle atonia, vivid dream imagery) into the transition between wakefulness and sleep:

Sudden weakness or loss of muscle tone without loss of consciousness, often elicited by emotion (cataplexy). 
Hallucinations at sleep onset (hypnagogic hallucinations) or upon awakening (hypnopompic hallucinations).
Muscle paralysis upon awakening (sleep paralysis).

The severity of cataplexy varies, as patients may have two to three attacks per day or per decade. Some patients with objectively confirmed narcolepsy may show no evidence of cataplexy. In those with cataplexy, the extent and duration of an attack may also vary, from a transient sagging of the jaw lasting a few seconds to rare cases of flaccid paralysis of the entire voluntary musculature for up to 20-30 min. Symptoms of narcolepsy typically begin in the second decade, although the onset ranges from ages 5-50 years.
Hallucinations at sleep onset (hypnagogic hallucinations) or upon awakening
Sudden weakness or loss of muscle tone without loss of consciousness, often elicited by emotion
Muscle paralysis upon awakening
Muscle paralysis after sleeping