Might be Restless Legs Syndrome, but your doctor, who may refer you to a neurologist to confirm it, is the one to tell you for sure. It can be a couple other muscle problems besides that, so that's how come I can't say for sure. I have RLS and the hallmark of it is when you lay down to rest or sleep, your legs start up. People describe the sensation differently, but basically the calf muscles tighten and you want to stretch them out, and the only thing that stops it is to get up and walk around. Very hard on a person because it wears you out, and yet when you try to rest, it starts up again. There are medications for it, diff ones help in varying ways, and there are several online organizations that have forums where folks talk about it with each other. Maybe someone else will post with those other causes of extremities jerking around.
Restless legs is one thing it could be and myoclonus is another, basically a hiccup is a myoclonic jerk, so any involuntary jerking could be a myoclonic jerk.
I have spinal myoclonus and it makes my legs and back jerk.
I recommend you see your Doctor as ggreg suggests, I have had this for nearly 4 years now and have had numerous tests which were arranged through a neurologist so it would be an idea to get referred.
All the best
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