I had a bout with the Girl Scout cookies a few weeks back when they first starting popping up. I, too, used to eat plenty of these quite easily. Now, they are pretty darn sweet - too much so almost. I get the pounding heart thing too from the sugar. I consider it good because my body is recognizing the subpar food.
Glad you are aware of your eating experience and how you feel, and I'm glad you aren't beating yourself up about it. I consider times like those just little experiments that serve to show that sugar does have effects and that going back to primal after feels relieving.