I had my first one just a few days ago! Totally my fault. I've been training my gelding, and our first rides have been mostly around the cornfield across the road. By himself, he's a perfect gentleman.
The neighbor girl happened to be out riding her massive QH at the same time, so I asked if she would like to ride with us.
Normally, Siaga and I go around the field counter clockwise, we went clockwise that day. So he was introduced to two new things at once, rather than just one. We were going along mostly fine, with him being a little antsy, and we came to the irrigation ditch.
He stopped and put his nose to the water to make sure it was safe, started to walk across it, spooked, and jumped it. I have never jumped anything and wasn't expecting that responce as he normally walks across the ditch. So then I'm off balance and don't have a good hold on the reins and he's trotting off and I'm slowly bouncing to the side... and then he goes into a canter (first canter on him) and the saddle, for heaven's sake, starts sliding sideways! Then he's galloping (my first gallop ever... lets see, first jump, gallop, AND fall...) and the saddle's still slipping so I bail. I remember looking down at the ground and seeing it flying by and then looking up and seeing my foot coming over his back and the reins flying and his mane waving and the sun shining through it, all in like, slow motion... then nothing. It knocked me out.
I woke up and got the horse and started walking home, but a few minutes later I must have went into shock, because I don't remember crossing the ditch again or untacking him or taking him to the barn. After that I couldn't remember things like why and when I moved home (about a month and a half ago) but it all came back to me. Thank god I had on a helmet!