How is energy related to blood glucose levels?

Low=low: You need a normal blood glucose to have energy! if your blood glucose gets too low, you will feel fatigued, shaky, and sometimes nauseated and confused. If you've ever done aerobic exercise without eating enough, and you've had the feeling of "hitting the wall"... That's low blood glucose!

Glucose metabolism: Glucose is the fuel for all cells. Low glucose levels mean not enough fuel for cells. Insulin is what makes the glucose enter a cell. If you have Insulin deficiency (type 1) or if there is Insulin resistance (type 2) -again glucose levels are high in the blood but not able to enter the cells (again the cells are starved for glucose)-one would feel tired