cat·a·plex·y / ˈkatəˌpleksē/ • n. a medical condition in which strong emotion or laughter causes a person to suffer sudden physical collapse though remaining conscious.DERIVATIVES: cat·a·plec·tic / ˌkatəˈplektik/ adj.

cataplexy (kat-ă-pleks-i) n. a sudden onset of muscle weakness that may be precipitated by excitement or emotion. There may be total loss of muscle tone, resulting in collapse, or simply jaw dropping or head nodding. It occurs in 60–90% of patients with narcolepsy.