That is crazy! I'm glad to hear you and your friend, and her horse were safe!
One time me and my horse were at a regional equestrian meet. And it was a weekend shows, and it was a miracle that we had made it to regionals! Well our school's policy is that we weren't allowed to show on sundays since we are a Christian school. So before we left I decided to take my boy out for a couple of laps around just to stretch his legs (bareback) before we headed home. Well he had been a little antsy, and so I put in his reining bit (one that he knows NOT to run through at all!). Well my two-man partner also came in and decided that she was going to start cantering... right next to me and my "hot" horse (even though we had just been walking.. crazy horse!) well once she took off, so did my big boy. And i'm not a very good bareback rider so I was a little concerned, but was able to slow him down to a very bumpy and fast trot. Well we rounded the corner, and all of the sudden he TOOK OFF! He started flying down the fence! Nearly hitting some of the other horses! I on the other hand was trying with all my might to get him to stop and hang on for dear life. Now the arena we were in was of fairly good size, though it seemed smaller when he started flying towards the gate. Right before he hit the gate he turned, sending me saling, hitting the gate, and doing a backwards sommersault and landing on my back with my legs up in the air (must've looked hilarious). As soon as it was done, I checked him over and nothing was wrong, not scratches or anything! And I was fine to! It was strange though because as soon as the "ordeal" was over, he went back to being his normal lazy and gentle self! It was mind boggling! About an hour later, the announcers said they found a horse shoe from the arena we were in.. turns out it was Rudy's. The horse shoe was bent and all the nails were still in it! See, what had happened was when he was doing his weird trot, he over stepped, and tore out his own shoe, causing him to go running wildly because of the pain. I was so happy that is was just his shoe, and nothing else!