Hi, Thanks for writing in and sorry to hear about your injury. Hope you are not in much discomfort. Falling on the back can send the back muscles in to spasm. This happens due to sudden contraction of muscles during fall and can be a source of pain and discomfort. It can last for more than a week. No fractures on X ray is a good sign. However, you need to apply ointment containing muscle relaxant and pain reliever to your back. If available you may also use a heating pad. Rarely, it is also possible that you have hurt your discs in the back region. A slight displacement of intervertebral discs can cause pinching on nerves and lead to pain that will not respond to usual medications. I hope you will recover in a week or two. However, should your pain show persistence then please consult your doctor again and if required get a MRI scan to check any spinal disc problem. Take rest and avoid heavy physical activity till you get back to normal. Please do not worry.