or Bigjumpers an idiot....
stick with the group. If you're afraid your horse might run away, talk to someone and have them be your "buddy" and stick with you...that was you're never away from all the horses, and theres someone to help you out.
If you horse DOES take off, sit UP, use the pulley rien and CIRCLE. Don't be afraid to "rip their teeth out" as bad as that might sound, you're in danger and you need to hrose to listen. Sit UP!! and put your legs on!!It'll keep you on and balanced

Also, give a lot of space between horses, or if you have "rusty brakes" then make sure you're behind a horse that doesn't mind if you bump into their butt a little. Watch the person a few horses in front of you, so if they're slowing down, you're already know whats goign to happen.