Justine, I don't know about the palpitations, but peppermint will relax the LES (lower esophageal sphincter) causing refulx. This is never a good idea, especially late at night. Probably not a good idea for Afibbers in general, given the relationship between gastro-intestinal issues and AF.
lisa
__________________________
So much of medicine is looking solely down the wrong end of the gun barrel, and that is really a pity for all of us---Shannon