I Have Experienced Six Episodes Of Upper Back Muscle Spasms

I have experienced six episodes of upper back muscle spasms over a course of several weeks. Each episode causes my blood pressure/puls rate to rise. The episodes last approximately 45-60 minutes before settling down. The second episode resulted in a trip to ER where I was checked/cleared for heart/lung issues and suggested it was from back problems so visited my orhtopedist who prescribed muscle relaxers and aquatic PT. Followed these instructions for the past five weeks. Last week I was awakened in the night with an episode. Called my internist who had me come in for blood work to check magnesium/thyroid. Last evening another episode occurred, lasting over an hour. Several minutes into the episode my pulse rate had gone to 133 even though the episode was decreasing at that time. Had been advised to seek ER help if it exceeded 150. Am at a quandry as to what is causing this problem. Any suggestions?