mahjong.

From the Economist's Hong Kong briefing:

Mahjong menace

Mahjong, a game of skill and chance popular with Hong Kongers, may have unintended side-effects. A report in the Hong Kong Medical Journal has linked the pastime to epileptic fits. The study of 23 patients who experienced seizures mid-game found their epilepsy to be associated exclusively with the playing of mahjong. The authors suggest that the game’s mental demands, coupled with stress of betting and the exhaustion of marathon gaming sessions, can combine to trigger seizures. The best prevention, they say, is to avoid playing or watching the game.

Gotta go tell my moms.