I know what you are talking about. The same thing has started to happen to me. I told my PM dr. about it and he gave me Requip the same thing they give to Parkenson patients and RLS..restless leg syndrome. It has help quite a bit. It doesn't make it go away, but at least now I can sleep on the bed without thrashing around. I don't really know what ppl call it. I just tell the dr. that it is like a cramp that has started but doesn't get to being an actual cramp, and that my legs jerk around and off the bed. It ususally happens when I'm resting. This does sound like what you are experiencing. It is part of the rsd according to my dr.
I know others with more knowledge will be one to help you more than I have.

Hugs
Mary