I read your post and thought I would just add my two cents in...lol.
I was not there to witness your acciddent so therefore I am not totally sure what happened but this is what I believe.
I have ridden my share of different barrel horses in the past as well, and when running home I have found that the best thing to do is run your horse straight at the fence or down the alley. When you are nearing the end of your running and past the timer line getting closer to the fence, my personal opinion is to sit deep in you saddle place one hand on the horn with your other on the rein and let the horse collect up, sit down and stop on its own. You do have to make sure that you sit a little while in advance though so that your horse has the oppurtunity to prepare for the stop. I have found that this works with many of my different horses, they all run in different bridles, and some are more hot/fast than the others.
I do not believe in letting your horses turn at the end of your run, only under a very certain circumstance. I feel that if you always let your horses turn at the end of your run, you horse could create a bad habit and start interpreting the turn too early. I have seen horses do this many times before they are even past the timer line because they have gotten away with it too long. I also feel that it is way more dangerous than just stopping straight.
I totally know how you feel with your wreck as I had been in a similar position 2yrs ago. I was at a barrel race at a really nice indoor arena. The indoor wasn't a huge arena, but a pretty good size pattern had been set up to make the most out of the arena size however there wasn't a whole lot of stopping room. A 5-6 foot plywood type wall had been set up to be used as a stopping fence. I sat on my horse while the barrel racing was going on and watched as many people turned their horses at the end of their run and I vowed that I wouldn't do it. When I made my run I was coming home from the third barrel and passed the timer line, I think I may have sat down just a little too late not giving my horse enough time to stop, but still to this day don't know exactly what happened. My horse slide aways and then with no where to go at the last minute tried to bail the fence with no success. I was thrown over the wall and when I looked up the horse had its frontal body over the fence as if it was going to land on top of me, luckily for my sake it fell backwards over the other side of the fence opposite to me. Anyways despite this, I ended up pulling in the third fastest time in the open and winning the youth division. A nice buckle, and some prizes as well as some good money so it was worth it.
My horse was sore for a couple weeks after that...but she ended up being just fine.
I had never had this problem before and sometimes I think fluke things like this just happen. I also rode a horse before that had a big engine and on the way home, the more you got on his face the harder he would run. By letting him stop himself it taught him to really back off and now he is great. I think just stay with how you normally ride him, chances are he will remember the wreck too and really be more aware of things at the end of his run.