Sometimes after a hard Thai Boxing class for example containing long heavy-bag sessions or sparring (usually something consisting of intervals with explosive motions) I still feel tired or exhausted the next morning. It's hard to get up and have the feeling i take longer to wake up and be able to fully concentrate in the morning. Especially if i have not trained for a while.
The obvious conclusion is not to train too hard, sleep enough and take it easy after breaks.
Nevertheless it makes me think about what kind of techniques there are to aid recovery. Maybe things like a hot bath, certain minerals, etc...