The two that immediately come to mind are:
When I was running poles, and my horse tripped up going around the end pole, which he had never done before. It slammed me into the ground over his shoulder landing head first. When I tried to get up, I couldn't, so I was taken to the hospital in a meat waggon on a board and in a c-collar. I managed not to break anything or suffer a concussion. I was extremely lucky. I was also extremely sore the next morning.
The other was one time I was riding horses for a couple, and I was running behind with one of the younger horses, so the woman saddled my next horse or me. What I didn't notice was she put a cavesson (sp?) on this mare because she gapped if you picked up on the reins very much at all. I usually rode her using leg signals, so I only picked the reins up to adjust them for her. I checked her girth, and stepped on. I picked up on the reins to adjust them as I asked her to turn around with my legs. And boy did she come around! I dropped the reins, said whoa, and she stopped short. The only problem is we were on grass, and all four feet slipped out from under her tossing her onto her side with my leg pinned under her. She rolled over the top of me, but I managed to bend over where the saddle horn wouldn't get me in the stomach. I also managed to ride her back up again. I stepped off of her, checked her over, and removed the cavesson and continued on with my ride. For about two weeks I thought I had managed not to hurt myself, but then my legs went numb from about mid-calf down, and it gradually ascended to where from my waist down was numb, and I could barely walk. I went to the doctor, and told them what happened. He didn't bother taking x-rays or nothing, and told me that it was all in my head! I went for nearly three weeks like this until my lower back popped one day, then I started getting my feeling back and the ability to walk normally. I was sore for nearly a month after that. Sorry the second one is so long!