Maybe it's just a combination of tiredness and muscle pain? I go to the gym regularly (well, once a week!) and sometimes need a day to get over my over exertion, I feel better because of it in the long run. "No pain, no gain" ;-)

I have also been pondering this question for quite some time. Apart from feeling dreadful if I'm too hot for too long, I've not been able to make any direct connection to exercise and relapses. I don't know about other people but I do find that the wealth of variables makes it hard to know exactly what effects certain things have. Being on a load of medication with varying side effects doesn't make it any easier either! D x