Why does diabetic people feel lethargy?

Your cells make use of glucose – sugar – for fuel. The hormone insulin controls the allocation and use of glucose in the body. In diabetics, due to poor production of insulin, the glucose is not appropriately utilized by the cells; instead, it’s floating around in the bloodstream, where it can’t be used as power. As a result, you may feel constantly drained. Just like a car that has no gas your body needs the sugar (like gas) to keep it moving.

Also, because your cells are starving for fuel they slow down or quit so that what glucose is available will go to the most needed spots - brain and heart. This is why some diabetics will take frequent naps or fall asleep when their blood sugar is too high or too low. Blood sugar has to be within a normal range for it to be normal in the cells. Too high or too low in the blood means the cells are not getting any.

Lethargy is an alteration in the consciouness of the patient. It is related to the increasing amount of ketones in the cerebral area due to lipolysis (destruction of fat to produce energy). Lipolysis occurs when the ATP of the patient is insufficient due to absence or insufficient insulin to digest glucose for the production of energy. Lethargy is an early symptoms of Diabetic Coma