Anyone can laugh in a group for 15-20 min without depending upon the Sense of Humour, Jokes or comedy. It combines laughter exercises based on Yoga breathing, which turns into real laughter when practiced in a group.
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.