Now, it's finally time for a long overdue post, namely the effects of Battle on Stress and Fatigue.
First off, HP lowering does NOT seem to have any effect on Stress or Fatigue. In fact, the effects are not tallied until the end of the tournament. As for the effects, battles causes a large amount of fatigue to a monster (duh) but it also lowers stress BIG TIME. It doesn't automatically elminate all stress, but it does cause it to drop sharply, it's also a fixed amount, not a percentage, so stress CAN drop to zero.
Here are the effects I found:
Win tournament: +37 Fatigue, -75 (!) Stress Do well in tournament, but don't win: +50 Fatigue, -62 Stress Do poorly in tournament: +62 Fatigue, - 50 Stress
Also, withholding praise from your monster can cause Stress to increase. The amount depends on the reaction.
Monster is angry: +8 Stress Monster is disappointed: +4 Stress
Curiously, withholding encouragement does not incur Stress.
Note that the exception to this is the IMa-FIMBA meets, which appear to cause more Fatigue than usual. I may get around to testing this at a later date.