Accidents can happen even with your best horse
I was riding my mare at the Big South Fork recreation area and had been dieting trying to lose weight. It was a hot day and I must have had a blood sugar crash because the next thing I know I was laying on the ground with my husband and friends surrounding me.
Although my mare was perfectly behaved, we were cantering along and I had passed out and slid right off my horse. Unfortunately I had forgotten to put my helmet on that morning and did end up in the ER with a concussion. I am ever so religious to remember my Troxel Helmet EVERYTIME I ride now... even on a very trustworthy mount.