AF is not a lethal disorder. It can lead to problems if left unmanaged, so it should be managed. But I'm talking about months, years...not a few weeks. You are worrying needlessly. The single most important caution is about the risk of stroke which takes place within a few hours of the onset of AF. Therefore he should be prescribed a regimen of anti-coagulant, whatever works for him....safely. A cardiologist would know to do that immediately. Other than that, the other problems come months down the road, and some of it is reversible if the AF is fixed.....fixed...not cured. There is no cure, but it can be 'fixed', especially via the gold standard treatment known as catheter ablation. It's a day procedure, and it works wonders to stop AF from happening most of the time.

I have a Fitbit. It monitors for AFIB while I sleep. Almost every episode I've ever had has started while I was sleeping. I also have a Kardia 6-lead. Any time that I wake and have a notification that I was in AFIB, I immediately check on the Kardia, and my Fitbit has been correct, every time. Having most of my episodes at night actually seems safer, and causes me less anxiety. Try to relax... AFIB is not a death sentence. Just stay on top of it with his cardiologist and EP. Hang in there!