Question about Yoga and back problems...

Question for people who do Yoga:
I have herniated discs in my lower back, although they rarely cause me pain anymore unless someone presses on them; however, part of the "cool down" (I can't think of a better term) portion of the Yoga class has me hug my knees and slowly roll from one side to the other on my back.
This was very painful on my lower back while I was doing it and still hurt for several hours afterwards.
Can I just skip this part, or is there a better way to do it to take pressure off my lower back? That is the only thing that hurt - everything else was fine on my back.