The feeling of longing for something, some great wonderful or exciting thing or event, without knowing what that thing is, or how to quell the feeling. Usually accompanied by either a near-total lack of energy or the presence of frantically aimless and possible self-destructive hyperactivity. Generally hangs around for a day to a couple weeks and makes everything kind of awful; very rarely is it resolved in a satisfying manner.
Originally referred to a blue cake seen on Star Trek: Voyager. (Making that cake and then eating it doesn't help cure the feeling.)
Oh man, I have Blue Cake Syndrome something awful today.
You're blue caking too, huh? I blame the weather.