Indulging the Creative Urge

Why do I always get the creative urge to write late at night? It's as though I have an internal creativity clock that turns on around midnight and won't turn off until SOMETHING is put down on paper. This is annoying enough in the summer when I actually have the time to indulge it, but during the school year it is simply frustrating. I feel like saying, "Yes, I KNOW that you want me to write something, but I just CAN'T right now! I have school to attend to and prepare for and if I don't get my sleep, even over the weekend, then I can't do my job to the best of my ability." But, as these things usually go, it will not be ignored, and so it would be useless to go to bed anyhow because I will just lay there mulling over the story points in my head for several hours. I suppose that I had better indulge the urge...