one of the reasons I ride with others is "Just in case". I mainly ride offroad, so the occasional off is to be expected. Especially as the only place on a ride that I excel is downhill. Luckily, in the 15 years I have been offroading, I have only had two falls that hurt.
Over the bars is not a common occurence for me, but it does happen occasionally. Last time was a couple of years ago when I was with a group of 5. As usual I was the last one in line along a very wet, very muddy track. Gradually the others showed me the line NOT to take as they slipped off the bikes or stopped in axle deep mud. Got nearly to the end of the trail with only one rider in front of me and he skewed off sideways into deep mud. Only 20 yards to go and only one route left to take through the ruts and a massive great big puddle. Power on and go for it. the other riders were cheering me on, when everything went a bit fuzzy. The Deep puddle had a big root in the middle of it. Front wheel stopped and straight over. The only thing I knew was that it suddenly got very cold, and as I have said, very fuzzy. The water was only 18" deep, but I did a perfect back flop straight in and fully under. Surprising part was that other than being covered in Clay, I was perfectly dry.
If you must keep falling off the bike, and then worry about it, get more practice in, but make certain you have others around to pick up the pieces. Or at least pick up the pieces when they eventually stop laughing