You have got to love it when a doctor says any type of heart test is "basically" normal. I don't like to hear that either, I want perfectly normal. My last ER trip ( doc sent me to get vitals done due to panic attack, his office was loaded) I had an EKG done...about the 10th one and the nurse who did it let me look at it. It said "marked sinus arrythmia"... since I understood any arrythmia to be a bad thing I almost fainted. I was panicky to begin with, and that did NOT help me any. The EKG also stated Normal EKG.... okay I was confused and the nurse was confused also. She didn't understand it... it showed a nice even rhythm. So the doc comes in and I grabbed him right off with what was wrong with it... he just grinned ( didn't appreciate the humor at that point) and said it was common in children and thin people to have this arrythmia lying down. The heart gets a little extra blood flow for some reason and it pauses longer between beats while filling with extra blood. Apparently, people who are sensitive to any changes in heart rate can feel it but most people do not.
I'm still amazed, since I thought any arrythmia was a bad thing. With my panic disorder comes a heart phobia, since it likes to palpitate and take off with a fast hard beat. So the idea that my heart doesn't beat "right" while lying down does nothing for me.