Hi Kaz,
Do suggest you get onto the Atrial Fibrillation Association (AFA) website and research this condition if you are in Britain - or even if you are not. You will learn something and so long as you learn stuff you are gonna be well placed to control your own destiny.
Next, AF is -in its simplest terms - a malfunction of the hearts electrical circuitry. While you have made a good start with a Cardiologist you really need to see an EP, an Electrophysiologist - a Cardiologist who specialises in the hearts electrical circuits. Again, if you are in Britain the AFA website will guide you to one near you.
I was diagnosed with AF at 65 - my daughter was diagnosed during her first pregnancy in her late 20's. It went away following treatment and returned during her second pregnancy a couple of years later. It has never returned and she keeps herself pretty physically fit and is into Thai Kick boxing.
At the time of my diagnosis I had never heard of this condition and had led a pretty fit life and apart from childhood ailments had never been ill, except for DIY accidents arising from my own carelessness, and the occasional digestive issues in my early thirties.
I too went through the 'Why me' - no answer! Not then anyway, research into family medical history shows a high incidence of strokes but there is no one in my family alive now who can describe the cause of these strokes. I have a second cousin who has had AF (I'm now 72, he is now about 74), and of course my daughter.
There is evidence to suggest persons with AF have a predisposition to it, now chuck in the genetics/family history it is possible to have a genetic predisposition to it. A faulty DNA perhaps. It doesn't just affect young peeps like yourself or my daughter it can affect marathon runners, olympic level cyclists, air force fighter pilots even, and others in their 40's.
You may find that alcohol is initself a trigger, for me it is food and since I've gone gluten free and wheat free and sugar free and partly followed the FODMAPS diet I have controlled my AF, no recorded AF event now since April 2015. I am on a range of meds and will be for life - BUT - I still work 3 to 4 days a week driving a tourist bus handling passengers heavy baggage, I'm active, go walking along the South West Coastal path here in Cornwall and pass my annual medical for DVLA for my bus licence EVERY year.
If you get prompt and accurate and correct treatment I wouldn't think you'll have too many problems that you'll carry through your life. An Echocardiogram should show any other heart issues - I had mine done and there are no other issues except now a slightly damaged left atria which will never repair and therefore make me vulnerable to a stroke in the future.
My food trigger affects the Vagal Nerve, a major nerve in the central nervous system which controls many of our organs, especially the digestive system and the heart. You could research that.
You talk of BPM at 75 to 90. I'm assuming you are talking about heart rate. If that were me I'd prefer to see those number down to around 62 to 70 and I wonder what your blood pressure is ?
Anyway, hope that helps Kaz - don't be scared - ain't gonna do any good. You are young enough with the right care from a good EP to get this sorted and live a good life, AND also you are young enough to get the benefits from future advances in medical science in dealing with this.
May the force be with you.
John