The medical term for low blood sugar is hypoglycemia. Hypoglycemia is a condition in which the level of glucose in the blood drops below what is healthy for the body. For most people with diabetes, hypoglycemia is when the blood sugar level is below 70 milligrams per deciliter (mg/dL) or 3.9 millimoles per liter (mmol/L) . However, the blood sugar level that is too low for an individual may vary, so it is important to check with a healthcare provider to determine the appropriate level. Hypoglycemia can be caused by several factors, including excess insulin, lack of carbohydrates, and increased physical activity. Symptoms of hypoglycemia include hunger, shakiness, anxiety, sweating, pale skin, fast or irregular heartbeat, sleepiness, dizziness, and crankiness. If left untreated, severe low blood sugar can be life-threatening.