I don't do yoga, never have. However I have a very good friend who has a quite serious back problem and is under the care of a hospital. She goes to yoga and the yoga teacher says he has sorted out 'loads' of people with the same issue (disc).
I am sceptical as I don't know how much medical training a yoga teacher would have and I would worry about my friend doing further damage unwittingly by following advice from someone untrained in the area.
Or am i too sceptical?