So sorry that rib is broke...bless your heart....I FEEL for you. If I were there I would make you some biscotti, bring a latte and swap stories with you.
I think your horse bolted because of the other horses just like others have said. Biscuit did that once...Horse exploded out of his shelter running towards us. Horses in paddock next to us turned and ran towards us too. Biscuit whirled around and took off....and I came off. Ugh. It was in the grass though so other than some bruises on my let I was fine. Now it makes me nervous when I think horses are going to explode out of something...
I am a sissy.
I got back on though. He had gone down to his own paddock about 50 yards away and I am sure his though bubble was "there was danger running right at us sister....I got us out of it and your big butt fell off...there is no hope for you!"
I mounted up and rode back to the barn which was a big pickle for me. I had always said if I came off a horse again I would be too afraid to ride. Well, I wasn't...but I am careful!!!
When you are able you will be able to get up and go. Work on desensitizing your horse but unfortunately, we can't desensitize for EVERYTHING.
Hope you are feeling better soon. Take care of yourself!