I have found that my crashes are usually because of an electrolyte imbalance, mainly low sodium. So, when I feel a crash coming, I grab the celtic Sea Salt , pour a bit on something sweet and down it goes.
Also, I've found supplementing a little zinc after a stressful situation helps as the body burns through zinc under stress. Be careful with zinc, though, as it will disrupt copper levels which we are finding is a big problem in AF. I haven't begun copper detox myself, so doing 11mg zinc every now and then doesn't bother me. ;)