Whiff... Had given you a excellent example.
I too had similar.. About 18 months ago I went into Fast AF..
Just prior I was feeling really unwell couldn't get out of bed as I kept feeling faint, contacted GP they thought it was Vertigo?
About a week later I went into Fast AF..really frightening contacted 111 totally useless.
Luckily I'm a Cardiac Physiologist, I got in contact with a Cardiologist chum, he saw me was admitted to CCU to get my Heart rate stable with meds, but didn't stop the AF so I had a Cardioversion 6 weeks later..
I have always known I have a small Hole in the Heart, but it has never caused me any problems.
However, back last summer I told my Cardiologist I was feeling sluggish, so my meds were reduced. Didn't really help so I had 4 day Heart monitoring done, to see what was going on.
Turns out my problem was due to Intermittent 2 degree Heart Block which now is the thought that, it was that, that caused my feeling unwell and the start of the AF.
So last July I had a Pacemaker, can't believe how much difference that makes.
I know I'm only about 1 % Paced, so far no AF seen on check.
Back at the gym , had a Hip replacement 3 weeks after Pacemaker was put in. Can't believe how much I was struggling before, now full of beans.
So hopefully you will be well and sorted soon.