I have never experienced that sensation in my legs, I have however, had it happen in the left side of my neck. It would start in my chest and rise up thru my collar bone and neck up into my ear always on the left side and last just long enough to scare me half to death and make me believe I was having a heart attack or something. There was never any pain involved but I would, understandably, have "panicy" symptoms immediately after. It would happen 4-5 times/night (always in evening or night for me), but it has not happened in several weeks.
Wish I could help you more. I told my now x-doc about it and he acted like I wasn't even speaking and just kept on talking about what he wanted to talk about. If you find out what it is or what causes it, be sure and post it!