Too much exercise all of a sudden is really, really bad for you. Don't try it at home.
The exercise in question involved a rather muscular guy sitting on top of me and me trying to throw him off me, and then the other way around. Don't get too excited, perverts, we had our clothes on.
It was fun, but I discovered at least 3894 muscles I did not know I had, and every single one of them really hurts now.