I’ve been doing yoga, both hatha yoga and kriya for almost five years now and I haven’t suffered any negative side-effects. In fact, I can say that they have transformed my life in a very positive way. I think the problem arises when people try things out from the wrong source or after they see something on TV or after reading some book. I was initiated by Sadhguru Jaggi Vasudev of Isha Foundation, and I can definitely say I haven’t had any slipped discs or broken backs ever since. There are a couple of videos on youtube where he talks about improper yoga and the hazards of it. You can get more details about Isha programs from their website www.ishafoundation.org The Dangers of Improper Yoga www.youtube.com/watch?v=bV7BrUs9HFQ The Importance of Proper Yoga Instruction www.youtube.com/watch?v=8V9NAtl2YAM