fatigue has a soft reset at the end of the season. I say soft because anyone who is already extremely fatigued doesn't just magically go back to 100%. However, nobody can go over 102% fatigue (the wis norm) at the reset. There's no 10 game buffer in the playoffs like in the regular season, which is why you notice the change more. Also, byes play a huge role in preserving fatigue, so it is really difficult to win a 'ship without one (because you likely will have to go through three teams that had them), but it does happen.
and nbafan, games played have nothing to do with this sim engine. It uses total minutes only.