This is what happened. I was working her in the outdoor arena, all was going well. Had been trotting her for maybe 10 minutes working on softness in the face and bending at the pole. A truck and trailer zoomed by going super fast and rattling super loud. She took off bolting and I pulled her in a one rein stop and she instantly gave me her head and slowed and stopped. We were then facing the trailer and she had stopped. I petted her, told her she was a good girl, then she ran backwards and flipped over on me. Completely extreme I thought!! I’ve had them buck and bolt, but never this.