I have this situation in my upper back. It spasms so tightly, but MRI showed nothing out of place there despite severe pain. I do have tarlov cysts in my sacral spine, but that shouldn't cause pain up that high. I am thinking that there is some myofacial disorder...connective tissue issues. My tissues contract so tightly it affects my heartbeat at times, makes me dizzy. Seek out a massage therapist skilled in myofascial release...this is very different than a typical massage for relaxation. There are also some unique therapists that do muscle and tissue release called Ortho Bionomy. There's a website to find therapists into this. There are also therapists out of the Barrel Institute https://www.barralinstitute.com that can help if this sort of tissue release. https://www.ortho-bionomy.org