Every once in a while one of my limbs experiences what I d describe as a subtle vibration or jittery feeling. Sometimes a muscle in my chest, sometimes in my arm or my calf and just the last couple days in my thigh. Is this something common or should I be worried. It seems random & has been happening for years. It never lasts more than 10-15 seconds at a time & never more than a handful of times in a day. It ll often be months in between such feelings in my nerves/muscles but never the same place back to back.