I don't normally hang out here -- my usual abode is the Prostate Cancer forum. but I happened to be passing by.
I had a bout of AF following surgery for colon cancer about two years ago. Three days out from surgery, while still in hospital, I was trying to do without the patient activated morphine drip for the first time. Then the AF started. Very fast heartbeat, with it seemed some big pauses where my heart stopped completely. But other than that, I felt fine, although not active at the time.
An amusing event that I still remember is that my irregular heartbeat really screwed up the semi-automatic blood pressure machine the nurses use -- it could not read my BP. It was some time before they found someone who knew how to do it the old way -- with a stethoscope and cuff!
I spent the night in the cardiac unit where they put me on a special drip -- after about 12 hours my heart returned to normal. I have never had AF before or since. The doctors said it was a side effect of the surgery and the drugs I was on at that time.