That's why I favor a very gentle practice, and mostly do home practice.

I have a few useful books, and have attended some classes on and off over the years, but I mostly practice alone at home, quietly and listen to what my body is saying, and when it's saying "this is going from a nice stretch into PAIN", I stop.

At the same time, people can injure themselves doing all sorts of normal things too. My step-dad once threw out his back sneezing. He was in bed recovering for almost 3 days after that.

I once sprained my ankle very badly getting off a bus and missing the curb.

So, "Be careful out there."