Dude...this may not be the place for a guy with your history to look for medical advice.
Which won't stop people from giving it, so I might as well check in. I had what sounds like similar symptoms about 1990. I was a runner more than a cyclist at the time, 6'4"/215, morning pulse around 42, sometimes in the 30s. First thing I noticed was what I guess I could call a "heavy" heartbeat, a pounding in my chest after just a couple of miles at a slow pace. My resting pulse shot up, literally overnight, to the low 60s, and my mile splits on a five-mile run increased by more than a minute. An ECG showed me in solid atrial fibrillation, which wouldn't convert with drugs or electroshock. I've been on warfarin for more than 20 years (no particular problems with it, by the way), and now that I'm in my 60s, I figure I'd be slow anyway, so I don't worry about that.
My cardiologist is my age, and until his knees gave up a couple of years ago, he was a marathon runner and long-distance cyclist. Having a doc who was doing the same things I was helped a lot. I've found that some doctors, especially young ones, look at a 55-year-old guy who wants to be active and just reflexively tell him to slow down because of age. My PC doc and cardiologist both are older guys who exercise, and they were willing to work with me to make things as good as they could be, rather than just telling me to slow down. if they SAID slow down, I'd probably do it, but so far they haven't.