I used to get this much more than now, so I know what you're experiencing. I believe it's related to "Adrenal Fatigue". The terms to search for are "postprandial" or "prandial" and "tachycardia".
Frequent urination is a sign of low aldosterone. (cortisol shunt -> low aldosterone -> hyponatremia / dehydration) Try licorice. (Look up dosing; start low and go slow.)
If large meals do this to you, eat small meals. Seriously, that's a standard recommendation for AF sufferers.