I get this a lot, for the reasons that Petunia mentioned. Last winter, when I was working lots of hours in another city, I also started getting them in my legs. I called my doctor, worrying if it was the beginning of a blood clot, and that's when he put me on Lexapro. Why Lexapro for a blood clot, you may ask? Well, he said that I keep coming to him with physical results of stress, and that the thought leap from "twitching in my legs" to "OHMYGOD I HAVE A FATAL BLOOD CLOT MOVING TOWARD MY BRAIN" was the final indicator that I needed to get ahold of my stress and anxiety.