Energy Loss and Fatigue is often a sign of diabetes. In type 2 diabetes, cells in the muscles, liver and fat do not use insulin, which is a condition called insulin resistance; affects 90 percent of people with type 2 diabetes. Insulin is a hormone used by cells to allow glucose to enter the cells, which is then processed for energy. Because your body doesn't have enough insulin or is losing sensitivity to insulin, you can't shuttle blood sugar into muscle cells. Thus, the body cannot convert blood sugar/glucose into energy and fatigue results. Blood sugar rises to toxic levels and you begin to excrete that excess sugar into the urine.