For me it's energy and creativity together. My cycle also plays a part. It feels weird when the moon is full but I'm in a more tired phase of my cycle or vice versa, but when both coincide together, I have such an extreme intensity of a high or of a low.

Don't get me wrong, there are days I enjoy being awake earlier and enjoy the sunlight or the day time, but the time I am most efficient and most focused and inspired is at night.