Well, at times when I'm playing chess and consciously forcing myself to think through a high number of contingencies really quickly plus, trying to dominate the other person (psychological effect), I can feel the blood pressure increase between my ears. The gears are turning and my head swelles up. If the game is really intense my face might even turn red. But in the 84-85 world chess championship match between Kasparov and Karpov I know Karpov lost a lot of weight. Indeed, there are times in a chess match where one's pulse gets as high as 160 bpm. Needless to say, it is very taxing on the nervous system when a lot is at stake (money, prestige, ego, or all of the above).