Afib intermittent issues when having Viruses or other health condition

I don't understand the nature or context of your second question wrt BP, so I'll wait to answer that one until I understand your question better.

I, as well as many other AF sufferers, found that I was more likely to have ectopy, if not outright AF, when lying on my left side, but in my case only at first, when hoping to drift off into sleep. In my case, while my heart might have been a bit cranky right up to bedtime, and often was when I was having an AF day, it seemed to calm itself immediately after I had my first drift-off jerk where I'd often come awake again for a minute only to realize my heart was in perfect and calm NSR. This happened with 100% reliability, and one of the Great Gifts by the Big Fella, I think. But, if I knew not to roll over onto my left side, I would often do so during later sleep with impunity, and would often awaken that way with a calm heart. So, for me, the effect was real when attempting to fall asleep, but once my heart calmed I was good for the rest of the night.

You can sleep on your back, supine, but it invites obstructive sleep apnea as we age and as we age-and-gain-weight. To counter this, sometimes a different pillow works, but more often a soft foam cervical collar does a good job of keeping the chin from falling toward the chest and causing the trachea to pinch. Also, an elevating platform bed, if you can afford one ($4500 or more) will raise the chest to a better level while still being comfortable. They also need a foam or otherwise bendable mattress. Or, use pillows to jack you up, but that isn't as sure of a thing, and can actually make things worse, including the sleep quality.