Light

Your hands, your eyes, your voice, your thoughts are your servants. ~Loretta Young

One of my other foibles of being a creature of habit is the inability to go back to sleep after light enters my eyes. In other words, I can roll back into bed as long as I have a conversation with my eyes closed. Fortunately in my room I have really dark blinds that I keep shut tightly when I go to bed, so it isn't that huge of a problem until the sun reaches it's zenith.