FWIW, I was entirely self-taught until a few months ago (when I started going to RL classes too). I've hurt myself a few times doing yoga, but it's only ever happened when I've persistently pushed for a pose and ignored warning twinges of pain or strain.

If you've got chronic pain or joint problems, you may obviously have different issues to navigate, but generally, you do get warning signals if something's not right.

And there are some online resources that have excellent stuff on alignment (and RL classes which are crappy at it).