This sounds like the same thing that happened to me. For about a year I would get this most nights -- just as I started to drift off to sleep I'd get sort of tremors, especially in my back, which often kept me from sleeping. They were really bad for about a week and then fairly bad for about a year. Now, six years later, I still get them every few months or so. During the daytime I often had twitches and other odd neurological things happening. I eventually diagnosed myself with a variant form of Benign Fasciculation Syndrome. (This after doctors gave me about a dozen diagnoses, ranging from terrible diseases like ALS to "it's all in your head.") The good news is that over time it definitely has almost entirely gone away. Caffeine makes it worse. I found a sympathetic doc who prescribed a small amount of Valium, which I would take on the worst nights so I could sleep. I only took 1-2 Valium per month. In my case I think one of two things caused it. I had a weird virus that caused dizziness, and which may have brought this on also. But the same day that it began I also had a tetanus shot. I've never seen it listed as a side effect of tetanus vaccination, but the timing is suspicious. Best of luck with yours. I think there's a very good chance that, like mine, yours is annoying but harmless and will lessen and go away on its own.