I too take magnesium in an attempt to stop muscle twitches (fasciculations). This was recommended to me by a neurologist after a couple of tests. My fasciculations started during a period of serious stress and anxiety (of the "I think I'm dying"-variety). They've never really fully gone away. Some nights I can't sleep because some muscle is randomly twitching all night. Magnesium helps, but so does staying away from caffeine and making sure to keep hydrated.

It is commonplace for people to eat magnesium supplements before taking certain central stimulants to decrease yaw clenching and gurning, not sure if it helps or not, but it is a thing.