Hi,
Many people experience palpitations for a short period of time when laying down, including, as you said, sometimes eliminating them by shifting to another position. You seem to be quite concerned about them. Have you seen your Family Doctor and expressed your concerns? He/she can do an In-Office EKG.
No one on this forum, not even the Doctors, could emphatically say that your heart is healthy without having done an examination, including an EKG. Though I would like to give you reassurances that all is well, (likely it is a benign condition) having it confirmed that your heart is healthy is always the best thing to do whenever anything unusual is noted. Many people get yearly physicals, not because they are sick, but because they want the reassurance that they are healthy. Doctors do find many serious things during physicals, such as unknown arrhythmias. My brother had cancer of a kidney (he survived) found during a yearly employment physical.
Best Regards.
Its always good to get checked out by a doctor, but I'm having this off and on for over 45yrs. Lots of people have that. My husband has it too, but is not aware of it, but I can hear it when I lay my head on his chest, both of us were checked out (for other reasons) and we have healthy hearts.
Since you say it makes you a little fatigued afterwards sometimes I would have it checked out to be on the safe side. The fatigue could be from worrying over it or it could be something that has to do with your heart.