I have been told that I have a herniated disc (L2-L3) and when reading your book, I noticed that there are cautions about doing some of the exercises with a herniated disc. I am staying away from Stacksitting, but it seems to be required to do Lesson 5, Using your Inner Corset. Do I need to skip this lesson altogether? I also want to work on Lesson 4, Stretchlying on your Side - since the injury I have is not as low as L5-S1, can I attempt this posture? Thank you very much!