I feel sporadically dizzy all the time, and usually I have the exact same response as you at first - "Crap, is this something bad?". I guess the answer to that question is that it could be anything. However, vertigo, dizziness, lightheadedness - any of those, are among the most common symptoms, as well as heart beat issues. My heart frequently beats very fast when I get up too quickly, lift something heavy, or pretty much do anything. I've had a complete workup with my cardiologist, who is not at all concerned. If you haven't had a checkup in a while, it might be a good idea to, but this does not sound at all serious to me. Fact is, the body is weird and it does weird stuff. I just think it likes to keep things interesting.