Below-normal levels of blood glucose, quickly reversed by administration of oral or intravenous glucose. Even brief episodes can produce severe brain dysfunction. Fasting hypoglycemia can be life-threatening; it occurs most often in patients with diabetes mellitus who mistime insulin therapy or miss meals. It also results from insulin-producing tumours, starvation, or metabolic disorders. Reactive hypoglycemia occurs when the body produces too much insulin in response to sugar intake. Symptoms range from irritability to confusion and seizures, leading to coma and death in severe cases.