Mine was when a horse I owned got loose and ran out onto an asphalt road - a main road - right down the drive from the barn. I was already on a horse, which was shod all the way around. Impulsively, I chased my mare. The gelding I was riding was going very fast and before I had the chance to realize how idiotic I was being, he went down. I hit my head on the asphalt and broke my glasses (which punctured me right above my eyebrow). My right ankle was crushed and my knee was torn apart as well. The gelding was fine - he hopped right up and went back to the barn. The mare I was chasing saw him and followed him -_- It was my first ambulance ride and I was extremely lucky I didn't have any head trauma. Just a very ugly black eye!
Here's photos - ye be warned! Very graphic! That's why I've only posted links.
I want to know about your accidents! Videos? Pictures? Let's hear/see!