Hypoglycemia, Medline Plus article.

You have sugar in your blood. Your body needs glucose, a form of sugar to have enough energy. After you eat, your blood absorbs glucose. If you eat more than your body needs your muscles and liver store the extra. When your blood sugar begins to fall, a hormone tells your liver to release glucose, in most people, this rasies blood sugar. If it does not you have Hypoglycemia ,
And your blood sugar can be dangerously low. Signs include hunger, shkiness, dizzines confusion, difficulty speaking, feeling anxious or weak.
Hypoglycemia usally a side effect of diabetes medications. Eating or drinking something with carbohydrates can help.
You can have low blood sugar without diabetes--- Have DR, call lab to measure bloood glucose, insulin and other chemicals that play a part in the body's use of energy.

source- Medline Plus