I have been watching physical fitness programs of genuine instructors yoga. Can they hurt me?

Sure. Yoga can be an incredibly wonderful activity. I practice regularly and love it. However, you can also hurt yourself in yoga if you do not have instruction or if you try to do something that you are not ready for. I generally recommend to my patients interested in yoga to go to classes and then to use tapes/dvds only when they have gained some experience and no what to do and what not to do.