Generally, not. If there is no underlying cardiac problems that may predispose one to atrial fibrillation, it would be unusual for stress to be actual cause; however stress can be the underlying to so many maladies, that one never says never. If one develops atrial fib, must look for underlying heart disease, and--even it none is found-be treated for it by cardiologist specializing in cardiac rhythm disorders.
Yes. Yes it is possible, especially if the heart is damaged, or enlarged.