That is so interesting as I have always maintained that night time brings on the arrhythmias and lying on my right side is a sure bet for it, especially if I bring my arm over my body too. The doctors listen without comment but I have given up lying on what used to be my favourite sleeping side. As to what the cause is, Jerry might well be correct that it causes more displacement but that it happens to others makes me feel it is not imaginary.
Thank you so much for responding to my question. The answer to your question is that it only happens when I am lying on my right side and then heart rate goes haywire with missed beats and heaviness in my chest. I have been recently diagnosed with Graves disease 9 2 yrs ago) but my thyroid levels appear to be within normal limits. I tend to blame many things on the Graves but this problem seems quite bizzare.
Does the irregularity happen on both sides or just one side? I think I have read on the community about some people have rhythm irregularity when of one side, but not the other or on their back/stomach. I think lying on the right side puts more physical displacement on the (left side) heart.. but I'm not sure that is true. My memory doesn't retain all the good information I have read here. Perhaps this response will get you more helpful inputs.
As for inhale, it is normal, I am told to the HR to speed up on inhale (I can't hear it in mine) in normal and is the body taking advantage of the fresh oxygen in the lungs.