see cardiologist and ask about sleep apnea
My daughter's PVC's wake her up from a sound sleep when they come in couplets or she is in bigeminy. Have you had an EKG recently to see if you have frequent PVC's?
Your question is too "simple", that it the answer is too complex to guess at.
That said, I'd make a couple of guesses:
1) you palpitations are present more than just when waking up, how do you know?
2) I think it is possible that emotional dreams can cause heart palps, do you remember any troubling dreams?
Have been checked by a doctor?