If you eat a big carbo meal for lunch, by 3 pm you are ready for a nap. Excess carbos have generated overproduction of insulin. As your blood sugar drops, your brain begins to fall asleep. Because the massive amount of carbos you ate drove your insulin level up and your glucagon down, the fats stored in your body can't be released. But you feel fatigues, so you crave energy and more carbos.
Hypoglycemic tendency is inherited, and often comes with a family history of diabetes.
Remember, insulin triggers an adrenalin response. Coffee, tea and colas stimulate the release of adrenalin, as does nicotine. All carbos stimulate the secretion of insulin. Fatty acids are actually the preferred fuel for building new muscles and for energy. A high-carbo diet means fat is deposited and it stays.