If a person with diabetes is not currently using insulin or taking a sulfonylurea, you likely do not need to worry about hypoglycemia. Drugs like metformin or thiazolidinediones generally do not cause hypoglycemia. However, there have been some reports of patients experiencing hypoglycemic events after taking just metformin and sometimes even without taking any medication for diabetes. So you should always be aware of its presence, even if its likelihood of occurrence is small. Hypoglycemia is usually defined as blood sugar below 3.9 mmol/L (70 mg/dl). However, the symptoms of hypoglycemia depend more on the rate at which blood sugar falls than on the actual blood sugar level. This makes a lot of sense. The body is very clever, and if it senses that your blood sugar level is dropping too fast, it will start to figure out how to correct it before it gets so low that you pass out. The hypoglycemic response is exactly one way the body tells you that your blood sugar is dropping. The symptoms of hypoglycemia are different for each person. As some of the measures to correct blood sugar are the result of adrenaline production: shivering, sweating, rapid heartbeat and a feeling of nervousness or impending doom. Some patients may also feel hungry, irritable or behave abnormally.