Got appendicitis the end of eigth grade (as in about a week before "finals"), so I had it removed. Pain started one night, became unbearable so that I barely got any sleep. Morning went to the emergency room, argued with some nurses so my appendix didn't blow while I was waiting around (still waited a few hours, though) and finally got in and had the surgery (last thing I remember was them telling me something about an "orange cocktail" they were injecting which would make me pass out).
Yeah, I think I was out of school for a week. Got some nice sympathy from my teachers, missed a concert (I went and watched it, though), and all was well in the end.