Bummer. I forgot and this thread has gotten long. Where on your back is the spasm? I have a chronic tightness in my right rhomboid, trap, and neck muscles. I recently found a very good masseuse and that helped immensely. In fact once those muscles were loosened, my entire back felt better.

So maybe massage? And finally, watch out on applying heat to a spasm. It will feel good when you use it, but will aggravate inflammation after. Best to use ice, or something like a TheraGun or TheraCane than heat.