So...  I was sparring with a friend from college the other day.  We used to practice Wing Chun - which is essentially a Chinese fighting style developed for close quarters combat with numberous targets.  Anyway, we're fighting and all, and dude tries to hit me with a roundhouse (Dragon Tail kick) to the head.  Instead of dipping back or just ducking, I do this spin move that leaves me sitting on my ass - which was supposed to happen.  Unfortunately, when I tried to come up, I hurt the hell out of my knee, and subsequently wound up getting kicked in side/arm when he followed through with the other leg.

The lesson here - martial arts hurt, and that pain increases exponentially when you are out of shape!