OK. Firstly,
don't panic. I've been there (actually, I'm still there) and I'm still cycling. I'm 64, I've ridden 5000 km this year so far, I can still ride over 100 miles in one day (admittedly only once a year). I'm asthmatic and I smoke and drink.
Anyway, for what it's worth here is my experience.
My atrial fibrillation went undiagnosed for rather a long time due mainly to my own self mis-diagnosis and my lifestyle.
In 2005 I was beginning to get very breathless on the bike. I put this down to my asthma getting worse and figured that exercise was the best method of treating it. (It had worked before when asthma was the actual problem) I never went to the doc because, let's face it, what smoker is going to go to the doctor and ask "I seem to be getting breathless when I exercise. What do you think I should do?"
Anyway, the breathlessness got worse and worse until I was having to stop every day 3/4 of the way in on my 5 mile commute, sit on a wall or something and gasp until I felt strong enough to continue.
What I didn't realise was that the breathlessness was not a lung problem but was being caused by the malfunctioning heart failing to deliver oxygen properly and the lungs trying to compensate.
So eventually I went to see the doctor, telling him that I seemed to be having problems with my asthma. He stuck a stethoscope on me, widened his eyes and called an ambulance.
10 days in the cardiac unit at Selly Oak Hospital.
The usual cure for atrial fibrillation is a cardioversion, but after my hospital treatment my AF became intermittent (sort of 2 days off, two days on), consequently on three separate occasions I attended a hospital appointment for this treatment and was chucked out for being in possession of a perfectly normal heart rhythm. (Ever woken up in the morning and hoped that your heart wasn't working properly? Sounds daft, but that that's how I felt before the third attempt)
Eventually, they put me on a seven day 24 hour mobile recorder (the guy said, "I can see when you cycle to and from work - left a bit early on Wednesday, didn't you?) A week of no showers, just strip down at the sink.
After seeing the results, they decided on an Ablation.
This is where they enter through the femoral artery via the groin and go up into your heart. It's a sort of chimney sweep affair with a Swiss Army knife on the end that has a camera and a miniature cheap zippo lighter. They check where the electrical current is leaking across your heart muscle and cauterise the shit out of it.
Worked for me!
OK, I'll be on flecinide tablets and either aspirin or warfarin daily for the rest of my life, but it's good.
The aspirin vs warfarin is my doing. Doc would prefer that I take warfarin, I but object. As a cyclist who fettles and someone who enjoys cooking, the occasional cuts are inevitable. Cuts that absolutely refuse to stop bleeding are shite.
Sorry, that was very long winded, but I took you at your word and assumed that you would want to hear everything.
Don't worry. You'll be fine.
The only difference should be that you need to get yourself treated before you become an emergency admission like me. Don't ring the doc. Make an appointment and see her/him face to face. Ask them what they are doing to get you back on your bike. Don't accept any compromises. Tell them "Cycling is what I do."