SO glad to see this post! My husband thinks I"m crazy, but I've been experiencing this for a little over a year. When it first started, it was only occasionally and I thought that the bed was shaking subtly, as if my cat was sitting on it and she was scratching herself. But after a few times of wondering why my cat was scratching herself on my bed every morning, I realized that it wasn't the cat (or an earthquake!), it was ME!
Lately, I shake for about 30 seconds everytime I wake up....whether it's from a nap or overnight sleep.
I have NO idea why or what the mechanism is behind it. Is it neurological? hormonal? muscular?? It is really weird. I could certainly live with it as a symptom for the rest of my life, but the "not knowing" aspect of it is what I find disturbing. I worry that it's a symptom of a larger problem, I guess.
I am glad to see that others have had a similar experience!