My daughter and I both suffer similar symptoms. She has been diagnosed with POTS I’m still waiting for my tilt table test. We both have muscle twitches mainly in foot and hand muscles but can be in leg and arm muscles last up to 30 seconds. You can actually see it jumping. If I didn’t know better I would swear it was something crawling around under the skin. It seems to happen quite often .then won’t happen again for a month.