Just a slip
I was riding an 18 hand Hannoverian, very seasoned horse. It was an early morning ride just after the arena had been watered. I was warming up and my horse slipped and fell. He pinned me down under him and I hit my head.
My trainer says I never "blacked out" though I don't remember anything from before my ride to when my husband got to the ER to pick me up. I was wearing a troxel schooling helmet and I thank goodness every day that I was! I am sure if I had not been wearing my helmet I would have had a lot more damage then my concussion and my broken ankle. My 6 year old son still has a fully functioning mother (after my ankle heals) due to wearing a Troxel helmet.