I've had ME for 18 years but for the first 16 years the only parts of me that would twitch were my eyelids and my big toe. The eyelid twitching would typically last for four or five seconds and would re-occur every few minutes. It tended to last over a period of several days but then would stop for days, weeks or even months. I'm not sure what triggers it. Mostly it was hard to spot but sometimes the big and uncomfortable ones would be obvious to people around me. I would normally just close the eye affected, it was mostly my right but not always, and wait for it to pass.
Two years ago, which coincided with a whole raft of new neurological type symptoms, other parts of my body decided to join in the fun, various toes and both little fingers being the worst affected. But I had other small flickers around my arms, back and legs. Often they'd only last a few seconds and wouldn't appear in the same place again. But sometimes they would go on for several hours. Thankfully, they seemed to have settled down a bit of late.
That said, because of this thread, I've just bought some some magnesium supplements. We'll see how that goes.