1. Loss of muscle tone induced by sudden or excessive laughter.
2. A sudden loss of muscle tone (cataplexy) induced by uproarious laughter.

Cataplexy is a debilitating medical condition in which a person suddenly feels weak and collapses at moments of strong emotion; such as, laughter, anger, fear, or surprise.

Laughter and other emotions trigger a reflex in persons that can bring many of the muscles of the body to the point of collapse.