Being struck by a spark of creation.
Call it a spark. Call it a Muse. Call it Divine inspiration. Whatever you call it, I'm always completely struck when it happens. I can be writing and trying to make a plot point work or a character stand out and suddenly the writing takes off on its own and something happens. Suddenly all the puzzle pieces fit together and I smile because I know it was something greater than I at work. When these moments happen, time stands still and I lose myself in everything I'm working on. I could totally die happy afterwards.