I had an "oh crap" moment today on a trail ride, we were out with four other riders and a one-horse-open sleigh and we stopped to re-arrange the order (because the sleigh was having trouble with the deep snow) and my friend's horse Pearl, decided to have a roll. Luckily my friend managed to get Pearl up before she rolled over the saddle. Then Caleb decided Pearl had the right idea, and he decided to roll. I've never been on a horse who was about to roll, and I sort of jumped over him as he went down (lucky I have emergency stirrups). I was trying to get him up and everyone was yelling and telling me what to do, and I was pulling his reins and not-quite-kicking his butt and after about three half-rolls I think he decided it wasn't worth being yelled at and prodded and yanked on so he gave up before he did a full roll.
The absolute scariest thing that has yet happened to me on a horse happened in July 2007 on the first morning of a weeklong residential camp. I was riding this very round little palomino paint mare, Princess. She was interesting because she hated bits, so I rode her in a long-shank hackamore, but she was extremely sensitive to the leverage, so the reins were attached to the part of the hackamore that the cheekpieces connect to, essentially, I was riding in a halter with very long bouncing metal shanks.
I was riding her western, and we were doing barrel racing (the clover pattern) she had the worst balance of any horse I have ever ridden. We went to take the last barrel and we had almost finished the turn when suddenly everything seemed to slow down, I became acutely aware of her leg sliding, her body falling and me suddenly having a horse lying on my left leg. All I could think in those two seconds she spent down on me was "Thank god my leg isn't broken!" I was already getting up as the councilors came running, they were yelling at me to stay down but I didn't care. Princess had wandered over to the fence and I went over and grabbed her, climbed aboard and pretty much galloped back to the other campers waiting at the start. The whole episode took less than three minutes.
Well by the end of the week (I insisted my parents need not be phoned) the inside of my thigh just above my knee was swollen to the size of a small cantaloupe. I was later told by a doctor that over a liter of blood was accumulated, and I had a damaged nerve which would probably never heal.
Me and Princess doing keyhole: