Why are mornings so sleepy?

I realize I didn't have the best sleep due to the fact dusty worked nights, but why oh why do I have to be tired and sleepy. Today I am a home ec teacher with not the best set up... It is warm in the class due to the heat being on! Ugh, I don't need heat! I was productive last night and vacuumed the floor, did the dishes, finished washing the clothes, and even painted my nails! Saturday dusty and I went grocery shopping and went to sam's and publix. I still have more cleaning to do, but it felt good to get some done.