Like "Diabetic ketoacidosis. This is when you have little to no insulin and your blood sugar gets extremely high. It can feel like fatigue, drowsiness, extreme thirst, a "fruity" smell to the breath. Eventually, if left untreated, it can lead to a coma. While the blood sugar IS that high, it is doing damage to the vital organs of the body. Simply put, when the body can't use the glucose in the system (due to the lack of insulin), the liver produces "ketones" that act as another kind of "fuel" for the body (it is produced by using fatty deposits)."