Well, I guess in ways you are right. Normally, an arrythmia will cause palpitations, but an arrythmia is consecutive abnormal beats that are sustained for at least seconds but more commonly minutes and it is abnormal. Palpitations can also be due to benign (normal) beats from the atrium or the ventricle that just come one at a time or sometimes two together and are normal for everyone to have as long as it is occurring in a structurally normal heart. So, in summary, palpitations can be due to a normal phenomenon or an abnormal arrythmia.
I am curious what the dr. means by making sure you dont have an arrythmia? I thought palpitations were an arrythmia?
This is a very common complaint among people who suffer from palpitations and there are many people on this forum who suffer from your same complaints. Normally palpitations are benign pre-atrial or pre-ventricular beats and everyone has them during the day it is just a matter if you feel them or not. Some people notice them more at night when they are laying still or in different positions like you state. I get them too it is just that I don't notice them often. They are totally normal in a structurally normal heart and it sounds like you have had multiple tests to look into them. Usually we would check an EKG, echocardiogram, multiple lab tests including a TSH and a Holter monitor to make sure you aren't have an arrhythmia. If the palpitations become very bothersome, we sometimes try medications such as beta-blockers or calcium-channel blockers to see if that helps but anxiety really can make them worse and make you notice them more.
Hope this helps. Good Luck.