This went on to bug me. I must know this person, thought I, because I've never come up with a character like this, and it's too detailed to be a composite. I must know her. But where from? Who was she, and why did I remember her without knowing who she was?
On the bus in to work this morning, I remembered where I knew her from, and it all locked in to place. But that's nowhere near as freaky/cool as having a person arise in memory unbidden, with no connections to anything else to remind you of who they were.