In my other sport, eventing, we have this most feared accident when a horse misjudges the height of an obstacle, jumps not high enough, horses shoulder get stuck at the obstacle (eventing obstacles are rigid, no falling poles like with show jumping... it's like crashing into a wall), but due to the momentum, the horse flips over and burries the rider with the full impact of 1300lb in move. https://youtu.be/4cYvm-EnjWQ
It's the kind of fall which causes the death toll in eventing - if the rider survives, then with severe back/neck injuries, collapsed lungs a.s.o. Those accidents occur usually at high level eventing where the horses are at their max capacity.
I've vitnessed twice how friends of mine had that type of accident and it's freezing the blood in my vains even now when I memorize the pictures in my head, how the huge horse flips over, belly up and burries the slender body of my friend. The anxious seconds when nothing moves, the horse struggles to get up, the friend still beneath it and you don't know if the friend will move...
yeah... I was freaking scared to tackle that same obstacle afterwards, and seriously rethinking pros and cons in the evening . But it's the price you pay for the joy of it. I decided that's worth it.
(Both friends recovered physically, ride again, but quit eventing)