Hi
My back pain was not severe, so I'm not sure my experiences are completely relevant to you. I initially discovered inversion tables as a year of sedentary living and working at my desk for long hours had left me with permanent back ache. I started seeing an osteopath and although that helped immensely, after a few days the ache would return. I had muscle spasms, flat spots and a slight scoliosis. That is when I tried an inversion table. The first time I used the table I set the inversion limit to 20 degrees and even this felt wonderful. The stretch i felt in my lower back was just so relaxing, until then I had not realised how tight my lower back was. It felt great while on the table but it took about a month for me to feel any lasting benefits. By then I had worked up to the 60 degree pre-set which I found comfortable to maintain for several minutes each day. Around this time I also began improving my core strength by working out with a flexi-bar. After several months I found my back ache rarely troubled me even though I continued to work long hours at my desk.
I can also say that many people with back problems such as prolapsed/herniated disks find relief from using a table. Whether a table would help you depends on the actual cause of the pain, how often you used a table and whether your lifestyle was seriously detrimental to the health of your back.
Pete