I always forget about this phenomenon in between instances. But when I have a brief period with less creative work than usual, the writing itch really does get stronger.
I'm leaving the draft of my novel alone for a week or so, and I finished another creative project the same night as that draft (details after that project is revealed to its intended audience). I'm doing other types of writing, but nothing that involves creating characters or telling stories. In the past hour, I have done the following:
-read the name Abby in a book and started imagining what type of character I would create if I ever created an Abby
-overheard a conversation between strangers and started wondering what kind of voice one of the participants would have in a novel
I've thought that way before, of course, but to have it happen constantly and unconsciously tells me that my brain is in a fertile mood. When I get back to my own characters in a few days, I'll be super-prepared to imagine new things about them.