I have had horses fall on me twice, once on barrels and once on poles. I have seen several people whose horses have fallen while barrel racing. I doubt it was your fault, sometimes accidents just happen. Just make sure you get back to barrel racing as soon as possible! For me, once I knew that both my horse and I were okay, I got back on and competed in the next pole class later that day. At first, you may be more nervous than usual, but if you don't get back on and face your fear it will just get harder with time. Good Luck!