I have never had this happen to me, but I know a man that had a horse that would often back up quickly when having a hissy fit. Once she was rapidly backing toward a 20 ft deep ditch. So we all know not to tense and pull back at this time, and she was ignoring his cues to go forward.
So he pulled her head around hard (think one rein stop) so she was basically looking backwards, and could see that she was 2 feet from falling in the ditch. Well, she didn't want to do that, so she immediately stepped forward.