Hypoglycemia is a low level of blood sugar. A person may tremble, feel nervous or jittery, break out in a cold sweat, have a headache, and feel sick to his or her stomach.

Blood sugar levels are measured in mg/dL. A fasting blood sugar level of 70 to 100 mg/dL is normal, 50 to 70 mg/dL is mildly low, and less than 50 mg/dL is very low.

If blood sugar, also called glucose, continues to fall, a person may experience mood changes, such as irritability, anxiety, restlessness, anger, or confusion, and symptoms such as weakness, blurred vision, dizziness, fatigue, and poor coordination.

Hypoglycemia may also result from taking certain medicines, drinking alcohol, or from a variety of health problems, such as not processing carbohydrates properly or having an enzyme deficiency. Sometimes the cause is unknown.

Treatment for a sudden (acute) episode of hypoglycemia involves eating or drinking some form of sugar to restore blood sugar to a normal level. Episodes of hypoglycemia caused by a long-term (chronic) health condition are treated the same way, but prevention of future episodes requires treatment or cure of the underlying condition.