I think that your problem could have been caused by a few different possible problems. First, it is possible that you were a bit dehydrated at the time. If you were a bit dehydrated, the act of eating (which causes a lot of blood vessels in the body to dilate) could have lowered your blood pressure slightly and cause you to feel lightheaded. Another possible cause of your problem is something we call postprandial hypoglycemia. This is a condition where your blood sugar suddenly drops after eat instead of increase like it is supposed to causing you to feel faint. This can occur in a couple of different situations. First, if you have diabetes and take insulin before meals, these symptoms could be a sign of something called diabetic gastroparesis. This is when your stomach does not allow the food to get into your small intestine so the sugar that you eat doesn't get absorbed. This causes your blood sugars to drop. Another syndrome called dumping syndrome can occur for a variety or reasons including a history of gastrointestinal surgeries.
I suggest that you schedule an appointment with your primary care physician
to discuss these issues. If your doctor
thinks that gastroparesis or dumping syndrome, then you may warrant referral to see a gastroenterologist