My fastest crash was going down a hill on a gravel road. My bicycle hit a really loose patch of gravel, skidded out from under me .... and I went down on my left knee and hand. I had a lot of gravel imbedded in my knee, and I was scraped in varying degrees, almost all the way down to the ankle.
When I went to clean it out, I was in so much pain, I was actually convulsing. I was on tour and camping at the time, and there weren't any medical facilities around. In fact, the next night I was bush camping in the middle of the jungle ... and trying to change the dressing with only the medical kit I had and cold running water.
That was mid-December. I've still got quite a nasty scar.