I'm sorry to hear that you have Atrial Fibrillation.

Here is an excellent link that you can read up on it.
http://www.emedicinehealth.com/atria...article_em.htm

The good news is that when treated properly, it rarely causes serious or life-threatening problems.

Maybe it would be best to talk to your boss about cutting down your work load until you have this under control.

Take care and wishing you all the best David.