What Causes Muscle Tightening In The Left Arm After Discontinuing Pain Medications?

Hey, I m a 57 year old female, recently being forced off my pain meds and in the last few days have had several periods of time where I suddenly could feel a tightening of the muscles in my left arm and I have been unable to move it until the sensation goes away. It lasts anywhere from 30 sec. to a few minutes. I also notice I feel a little nauseous right before this happens. I am in an enormous amount of pain (chronic back pain) and I m concerned that the stress of the pain and being forced off my meds is creating a more severe problem, like stroke? Heart attack?