What could be causing anxiety-like symptoms after eating?

Vagal nerve overstimulation.

Sometimes its not anxiety, sometimes its fatigue. This one, at least, is something that most people get. Ever heard people talking about "food coma"? Of course, the anxiety part isn't so common, and I'd still be curious about that if I were you. But don't start thinking of the fatigue as a symptom of something dreadful when it might just be a standard quirk of the human metabolism.

I would say see a second doctor. Also, I suggest that you keep a food log for a while and see if you can spot the food(s) that might trigger the events. Record what you ate, and then a little after eating record how you feel. A few weeks of that should be illuminating and helpful to your doctor.

I had similar symptoms to that, when I had my ulcer. For me it was usually in the period of 30mins to 2 hours after eating. I slowly learnt which foods would trigger it, and which foods would not. For example, potatoes, onions and pastry were on the very high list. Anything to heart beating "loudly", heart in throat feeling, feeling exhausted (never passed out though), hot/cold episodes, during the worst times.

Do you get cramps in your stomach or have gas after eating?

I second the food journal suggestion. It might surprise you.

This might sound silly, but do you drink enough water while eating or just in general? I had a Holter because my last doc thought I had something very wrong with me with my very fast standing heart rate...and then my new doc realized I was just dehydrated all the time. Oh, and navratan korma does this to me for no good reason, no matter what. I just avoid it now.

Please consider having your thyroid checked. Your symptoms sound similar to mine when I had hyperthyroidism.

MSG has this effect on me, as well as large amounts of refined flour. My body feels hot and stressed out, my heart beats fast, and I'm anxious. Then it passes and I feel exhausted.