I'm trying to understand your comment about the heart failure being a proximal result of AF. That is to say, it happened, so the AF couldn't have gone on for long. In fact, heart failure doesn't typically happen in untreated AF patients for many months or years. There really is no practical way to attribute heart failure to any coincident AF because the two are only somewhat causally linked; there are other disorders that can lead to heart failure, such as defective heart valves and a poor ejection fraction.
Even so, my first incident of AF didn't leave me feeling unwell, but the second incident, about six weeks later, had me puffing and feeling like I was in serious trouble, at which the ER staff rushed me right in, no triage necessary. I can't explain that one bout of AF and how it affected me because two years later, when things had been in good control and I had been largely free of even intermittent/paroxysmal AF, suddenly I began to get lots of AF. But none of those many events, maybe 100 over the next year, left me feeling the same way, out of breath, faint, feeling of doom, etc.

I hope my comment isn't confusing...I intend only to point out that, if he does have heart failure, it would mean that it was from another problem, or that his AF,...IF...it was the cause, must have been uncontrolled, undetected, and in place for months, possibly well over a year.