Any of these reasons can cause a diabetic's blood sugar to drop dangerously low. Blood sugar is generally considered "too low" when it is 70 mg/dL or less. Symptoms of low blood sugar include:
Low blood sugar can happen suddenly. Usually the symptoms are mild and you can treat it by eating or drinking something with carbohydrates (bread, fruit, fruit juice, hard candy). If left untreated, it can progress to much more serious problems like seizures or a coma. It can even be fatal.
If you notice symptoms of hypoglycemia, you should take steps to increase low blood sugar. Regularly monitor your blood glucose to ensure it stays within your target range. It is especially important to check it if you miss a meal, eat less, or exercise more than usual. For someone with diabetes, low sugar can be serious so it's better to monitor your blood sugar and try to prevent hypoglycemia from happening at all.