I have had a couple of unprovoked back issues. The worst was a couple of years ago, I couldn't get out of my car. Two paramedics had to manhandle me out. I'll be they were glad I was only 125 lbs! Anyway, the solution to the problem was ibuprofen and lots of it for 10 days. However, this was under doctor's advice and this was for muscular issues only. Riding can actually be quite helpful to a sore back, as it encourages movement and helped me alot. But again, with a grain of salt. I was on a calm horse, walking only, in familiar areas... safety, safety...