About 5 years ago, I had a crash on my bmx, where I snapped my right collarbone in 2 places, displaced it from the inside joint, displaced my shoulder and broke the tip of the socket, and sustained mild whiplash. I don't remember much at all, but from what I'm told, I jumped the last jump in the set, and nose dived slightly, and clipped my front wheel on the back of the lander which caused me to pretty much headbutt the ground. the only bits I actually remember from the entire day, was launching off the kicker, then black, then slamming into the ground and sliding for a bit with the front of my shoulder pressing against the middle of my chest, and then sitting in emergency for 3 hours. Oh, and this was the day before my QCS test haha.
...luckily, I was wearing a helmet. saved my life plenty of times now.