Can someone please explain why hypoglycemia happens when you are not diabetic?

The body overreacts: The body normally makes just enough Insulin but under certain circumstances it can make too much and so the glucose levels get too low.

Realize that true : Concerning Hypoglycemia without a diagnosis of diabetes is rather uncommon. But under times of heavy utilization(significant exercise) or significant carbohydrate restriction your blood glucose can float on the low side and give rise to many symptoms like weaknesses, irritability and headaches.