So I was on 8 miles in on a my 16 mile ride, I stood up on the pedals to accelerate from a stop then *metals crunching* the chain came off my Brommie. I think I was shifting, but I'm not entirely sure. I didn't think it was a problem with internal hubs since they don't use derailleurs. I'm around the time when I need my 100 mile tune-up. Do you guys think this is the problem?