Chess or no chess if your sick, unfit, or drugged? OK, stupid question. Wen sick or untrained your mind moves more slowly then if you wear fit and well, but sometimes it can be positive with a slow brain. Players, playing players they think are better then them have a habit of doing exceedingly stupid moves, but wen playing after drinking alcohol or if they are slightly sick, they play an average of up to 20% better moves, increasing theire chance to win. Note that this is only if they believe that they are playing a lost game.

(information taken from "chack på liv och död") 

It is well known, that Tal played lot of his games slightly or more drunk. Maybe its just question of the amount, but when I´m playing after some beer or wine at the evening, usually can not believe on the next morning what I did yesterday :)