I had brief (1-2 minute) A-Fib episodes every few years when I competed at a high level (age 18-30). Usually in extreme heat, often after a heavy meal and dehydrated while running hard. It got more frequent in my 30s, and at about 40 I had one that did not covert on its own and after a few days I went to the hospital, went on Cardizem (mild drug that lowers the pulse, not as drastic as beta-blockers) and I was also on coumadin for a few months to protect from possible clots as a result of being out of rythm for a few days. I stopped the Coumadin but have taken 180 mg daily of cardizem ever since and have fortunately not had problems except a couple times when I forgot to take my meds. I am able to train hard but my max pulse is now around 165-170. Maybe it's higher but by the time I get a 6 second count at the end of a hard interval it's rarely above 160, and it comes down to under 100 in a minute. This is due to the medication. I'm sure this affects my ability to go fast and I am gasping for air after a final sprint in a way I never used to, almost like I have asthma, but I just can't move the oxygen fast enough. But I'm alive, I train hard, I place well in trail races and triathlons (top third of the 40-44 at the Wisconsin ironman), and qualified for a U.S. race walk team trip (for the first time in 15 years) to the biennial Pan Am Cup in Peru next month by placing 4th in the US 50 km champoinship in a less than stellar time. I have been lucky. Some people have not been able to control theirs with medication and it can become a debiliatating, crippling problem. There are new surgical remedies where they scarify (burn) the short-curcuitng routes of electrical signals that make the heart beat like crazy and out of rythm. Mixed success rates with this procedure, called ablation. Your cardiologist has no doubt told you all the options.
Let me know if you have more questions, although everyone's experience is different.