Yes back spasms can be a huge part of tms. My advice is different from others because some will tell you to ignore them and that can work but I like to massage my back really vigorously and then take long deep breaths to relax myself. Then I check in to see if I'm upset about anything. Did anything specific happen before the spasms began? Check in with yourself and try to relax and not be fearful.
Yes, back spasms are one of the most common manifestations of TMS. I see this all the time.
There are several ways to deal with this. Dianna method is good, as is becoming more "powerful" and telling your brain that you will not put up with this any longer; as is simply ignoring the spasms and learning to not fear it.
Does this help?