Reactive hypoglycemia is low blood sugar that occurs 3 to 4 hours after eating a meal. Symptoms include hunger, weakness, shakiness, lightheadedness, anxiety and confusion, according to MayoClinic.com. Reactive hypoglycemia requires a medical evaluation for a diagnosis.

Fasting hypoglycemia is a type of hypoglycemia, or low blood sugar, that occurs when the stomach is empty. Fasting hypoglycemia is diagnosed as a blood glucose level of less than 50mg/dL, according to the National Diabetes Information Clearinghouse.

Serum glucose, or sugar in your blood, is the mainstay of energy for your brain and body. Your body relies on the sugar your blood provides to function properly. If your blood glucose levels fall below a level that prevents your body from operating efficiently, it's called hypoglycemia, or low blood sugar.

Exercise induced low blood sugar, or hypoglycemia occurs when your body’s blood sugar is used up too quickly. Sugar, or glucose comes from the food that you eat and your body uses it as a source of energy during exercise.

Think of insulin as the key that unlocks the door to your cells. Your body uses insulin to allow glucose, or blood sugar, to gain entry to your cells, giving you energy. If your body has a tendency to make too much insulin, following a diet to prevent blood sugar dips can help to avoid harmful symptoms.

Hypoglycemia occurs when the blood glucose level is too low. Blood glucose level below 70 milligrams per deciliter is considered too low and could cause harm, according to PubMedHealth.

If your blood sugar levels drops too low, your body will send you signals. Shaking, sweating, feeling weak, dizzy or light-headed, being irritable, anxious or confused are all signs of a hypoglycemic reaction. Low blood sugar can happen even if you do not have diabetes.

Although the symptoms of a hypoglycemic attack can be very painful and include shaking, sweating and extreme hunger, you can reverse them. Attacks don't typically cause any long-term damage, unless the hypoglycemia goes untreated for long periods of time.