very tired

this past week I’ve been so tired, no energy to do anything except sleep work and maybe cook. I may have to have my blood checked, to see if my iron, Vit D and Potassium if ok. It sucks not being able to do anything except basically breath. Fatigue is something I never thought about until now. I never really understood it until now. How can you be tired from doing nothing but sleeping? How can you sleep all day, and still want to sleep all night.