I've had it for most of my life. It was at it's worst when I was pregnant. No amount of calf stretching helped. I believe mine might be affected by my digestion (specifically constipation or very dry stools) which makes it much worse, although I get it at other times. Always in the evenings at bed time, but I WILL get it on long car journeys or flights.
No itching, no burning, no ants. It feels like something is slowly pulling nerves in my lower legs. The longer it's allowed to pull, the more tension and the more nerve jangling it feels. The only way to stop the feeling is to move my leg, usually a kick or bringing my knee up.
This will NOT stop unless I get up and do something. It's associated with a sedentary lifestyle and it's recommended to do a little exercise an hour or so before bed.
Magnesium indeed helps a lot. 100% RDA tablets once a day. The added bonus is it also calms PMT.
My other cure will sound odd but I used it for years without fail. A bar of soap next to your skin will stop it happening and can also calm it when it's started after just a couple of minutes. Has to be a fresh bar, changed every few months. I put mine in my knickers, but you can use a sock or down your pyjamas or something.
Google it before you laugh!