I went to bed on Halloween with a headache.  Not a normal headache, though. It was the kind that made me wonder if bashing my head into the wall a few times might help.  It didn’t, and neither did painkillers. Or alcohol.  So I went to bed early on Halloween.  
But then I woke up again, almost exactly at midnight, and the pain was worse if anything.  I tried to fight it for a while, but it only got worse. Eventually I gave up, I got up, and I sat down at my computer and I started writing.  What the hell, right?  It was November, after all, it just seemed to make sense.  It even, almost, made me feel a little better.  So I just kept typing and typing, and the story just rolled out. I could tell right away it was going to be a big one.