Hi,
What you describe could be a condition called reactive hypoglycaemia, (hypoglycaemia is low blood sugar)
Reactive hypoglycaemia is possibly the most common reason for hypoglycaemia in non-diabetics but is often overdiagnosed. This form of hypoglycaemia is probably caused by an overproduction of insulin from the pancreas after a large meal with a lot of carbohydrates. The insulin can still be detected even after several hours, although the level should be back to normal at this time. This condition is probably most common in overweight people and those with Type 2 diabetes, where the large demand for insulin can sometimes cause too much insulin to be produced in the pancreas. There is some evidence to suggest that reactive hypoglycaemia can precede Type 2 diabetes.