I was just diagnosed with POTS and Mitral Valve Prolapse. I have had muscle twitching and various weird nerve pain and tingling off and on for about 4 years now (the muscle twitching started long before my POTs symptoms.) I had a million tests to look for MS, Parkinson's and other neuro diseases, but the doctors found nothing. My last neuro that I saw told me to have an MRI every 2-3 years to continue to look for possible MS lesions. The muscle twitching comes and goes for me. I can go for months at a time and not have any and then sometimes it comes back with a vengance. I also have fibromyalgia, but I really don't think that's the cause of the muscle twitching. I think it's some underlying cause that no one can figure out yet!