Those who have diabetes can become extremely tired if their blood sugar levels are abnormal. This can happen if blood sugars are too low or too high, according to the American Diabetes Association.
If a person has diabetes, it means he either cannot produce insulin, or his body is resistant to it. Insulin is a hormone that allows sugar into cells and gives the body energy. If the blood sugar is too high, it means the sugar is staying outside the cells, so the sugar has no way of converting to energy. If the blood sugar is too low, there is not enough sugar to energize the cells sufficiently, according to Diabetes.co.uk. In both cases, the body is not being provided with energy, and a person can feel very tired until he is able to correct his blood sugar levels back into normal range.