Yes. That is when I knew something was really wrong. I was in PT walking very slowly on a treadmill when it started. I couldn't stop and they laid me down, but I was shaking so hard for so long they called an ambulance. Resolved on its own by the time I got to the hospital. I do what the above posters do, cover up and rest. They are scary, though. They didn't kill me, and that is what is important to know. Just our crazy bodies acting badly!