Here is a quote from Wikipedia's page on "Made of Honor" movie (as it was on January 9th, 2011):
When questioned about Tom's sudden departure shortly before the wedding is to take place, Hannah informs Colin that Tom is just afraid of losing her. On the way home, Tom realizes that he must stop the wedding and goes back on horseback. Just when the priest asks for objections, Tom is sent flying off his horse and through the chapel doors. Seeing her best friend on the floor, Hannah rushes to him.
Is it clear for native English speakers from this passage that Tom's horse bumped into something (it was a fence around the chapel), so this was the reason why he was sent flying off his horse?
If I were to read this passage for the first time (without having previously watched the movie itself), I would definitely be puzzled as to why Tom was sent flying off the horse. But, perhaps, this expression ("sent flying off the horse") automatically implies to native speakers that the horse must have bumped into something.