From fasting 90 to postprandial 80? That looks really off. Your blood Sugar should rise after a meal and stay up for a good while.
But look at that graph. See that spike? How the food causes a blood Sugar skyrocketing followed by a plummet? At the bottom of the plummet your cortisol is supposed to help you come back up. We AFers don't do cortisol so well, so we sink farther than others after meals.