My worst/funniest fall was when I owned my own horse, he was an OTTB and had a tendency to be spooky and buck/bolt a lot. SO anyways, we were at a Dressage show and it was absolutely pouring rain and the show was held outside, the arena was super muddy. We were last to go and everyone before us kept telling us how their horses wouldn't go into corners, were spooking at the mud/wind so to be careful. So Denny, my crazy horse decides he is going to be WONDERFUL, he was working beautifully, coming round and going into the muddy corners without a problem.. until I asked for the right lead canter. He bucked, I flew off and landed in about a foot of mud in my nice white show breeches. I could've killed him!! It was actually really funny at the time, but I hurt my tailbone and still to this day (the fall was about 6 years ago) I have days where my tailbone causes me extreme amounts of pain.
Another funny one was once on the same horse, but during a lesson. We were jumping a little 2'6 course in the indoor. For whatever reason, Denny decided to swerve around one of the fences instead of jumping it. It wasn't even a bad refusal, he just kinda trotted around it but I wasn't expecting it AT ALL so I ended up doing a somersault down his leg and landing on my butt, LOL. The worst part was that I had a friend watching and as soon as I landed she stood up and yelled "NICE DISMOUNT!" Hahaha.