The first and foremost thing you should address is what is the pain being caused by. Take the time to get it found out, corrective exercise can do wonders for LBP. From personal and professional experience, if the LBP is caused by a disc issue and you wish to do yoga my advice would be to A: not do Bikram, since you cannot modify or slow it down (thus it would not be “Bikram”) as well as the heat issue addressed by a poster above, and B: seek a one-on-one session from a well-respected teacher who is informed of your specific injury-cause, symptoms, and etiology. After that you will have modifications you can do when the rest of the class you are attending is doing their routine. Where I live there are actual classes designed for students with disc issues and LBP.