Convulsions caused by a combination of sexual stimulation followed by uproarious laughter. Sexual stimulation increases tension and primes the body for release. The unexpected humor causes the aroused body to convulse with laughter, sometimes resulting in an unintended climax.
Derrick: "Oh, man, that girl’s pole dancing routine was so funny I almost had a humorgasm."
Dalton: "I know, right? Excuse me, I have to go change my underwear."