sg,Good Morning! I can see why you have questions and I will try to touch on a few of your questions but be sure to advocate for yourself and ask you Cardiologist/PCP these same questions as I am not a physician. 
According to the information from the University of Iowa Hospitals, Atrial fibrillation is associated with many cardiac conditions, including cardiomyopathy, coronary artery disease, valvular heart disease, ventricular hypertrophy and other associated conditions.
Some people have atrial fibrillation with no obvious source or associated condition. This is more frequent in younger people and it is called "lone" atrial fibrillation. It is likely that people who have this form of atrial fibrillation have had some inflammatory process or trauma to the atrium.
One form of atrial fibrillation that is treatable is so-called paroxysmal atrial fibrillation. This form of atrial fibrillation is more common in younger people and in people without serious underlying structural heart disease. In fact, this form of atrial fibrillation often occurs without any other underlying heart disease present. This paroxysmal form occurs when episodes of atrial fibrillation come for a short period of time and go away suddenly, to return later.
Caffeine and intense exercise are some of the triggers for irregular heart beats and in particular, atrial fibrillation. It is important to try to relate any irregular heart beat and the presence of atrial fibrillation to what is going on at the time.
Resource: Brian Olshansky, MD, Professor of Internal Medicine
You are decreasing Multaq with a follow-up heart monitor study. I suspect the monitor 3 weeks after your decrease in medication is to see how you tolerate the medication decrease.
I hope this info helps you but remember HealingWell should never take the place of your physician.
Let us know how you are doing.
Kindly,
Kitt