Wow, no answer since January 23? 2021? I an old-timer in may ways, including on this board. Haven't visited much in recent years.
Not familiar with the meds you're on, any heart rhythm specific? 45 is rather low, and the complexity of sleep issues complicates the subject. But I felt it worth the effort to say someone is reading your concern. I have suffered from long term atrial fibrillation, so my problem is opposite of yours, I'm lucky if I get below 70 when resting, and that's with beta blocker which slows heart rate. Back tot he point, if the meds you are taking are prescription, by all means discuss with the prescribing physician ... or if not, best to get a check up by at least a primary care doctor.