If they start out with, "How are you today?" say, "Why do you want to know?" Or you can say, "I'm so glad you asked, because no one seems to care these days and I have all these problems, my sciatica is acting up, my eyelashes are sore, my dog just died...." When they try to get back to the sales process, just continue on with telling about your problems.
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.