The level of sugar in the blood being lower than normal is called hypoglycemia. This problem is found in most of the people who take medicines for high sugar. However, those who do not have sugar or who do not take any such medicine, their sugar level can also drop suddenly. If seen, lack of sugar in the blood is not a disease in itself, yes it can definitely be a sign of some internal problem.
Read More - (First aid for low blood sugar)