I have heavy palpitations as well, but mine are likely related to a hormone imbalance. I have a nodule on my thyroid and have been told that an imbalance in hormones can cause heavy heartbeats. In my case, they've also been blamed on higher than they should be insulin levels and being overweight (another hormone-related issue).
I'm sure there are other causes as well, which your doctor would be able to tell you, but this is all I can share with you from my experience. I'd talk to your doctor about it just to be safe and as Sarah suggested, go to the ER or call your cardiologist if they last.
Wishing you well,
Laura
If its still bothering you go to the ER or if you have a cardiologist, call them. It could be caused by medication or us something new. Any excess caffeine intake?