My Shadow at night

I have a little shadow that goes in and out with me. And what can be the use of him is more than I can see.
He is very, extra ordinary like me, from his heels up to his head. I see him jump before me,  when I take the leap to bed.
One morning very early, before the sun was up. I rose and found the shining dew on every buttercup.
Then, noticed that my lazy little shadow like a silly sleepyhead, had stayed at home behind me, and was fast asleep in bed.