I have experienced almost constant muscle twitching in my left upper arm. I have tried massage, relaxation, stretching. At times is stops for several minutes, often times it's almost repetitive like a heartbeat. I have a history of muscle, tissue pain, never formally diagnosed, however an MD I worked for previously told me it may be fibromyalgia. I am a 50 year old female, slightly overweight, with dx of depression (20+ years), otherwise no major health issues.