Hypoglycemia occurs when the level of glucose (sugar) in the blood is too low. Normally, your body keeps your blood glucose within a concentration range of 4.0 mmol/L to 8.0 mmol/L (about 70 mg/dL to 140 mg/dL). In order to do this, the body has mechanisms that involve the hormone insulin, which is made by the pancreas, as well as several other hormones.
When blood sugar levels rise, the pancreas responds by releasing insulin to encourage the movement of glucose from the bloodstream to the cells. Insulin lowers the amount of glucose in your blood by signalling the cells in the body to use the glucose as fuel.
Your body uses glucose as its main fuel. The brain requires a constant supply of blood glucose and will signal the adrenal glands to release two hormones called adrenaline and cortisol whenever blood glucose levels are low. The adrenaline and cortisol then signal the liver to convert the carbohydrates it stores (from the foods we eat) into glucose and release it into the bloodstream.
The pancreas is also involved in raising blood glucose levels if they fall too low. When blood sugar is low, the pancreas releases the hormone glucagon, which increases blood sugar by signalling the liver to convert stored carbohydrates into glucose and to create new glucose molecules from other substances (such as amino acids) in the liver. If these mechanisms don't work properly, the blood glucose remains too low and the brain won't be able to function normally.