Dreams. When you have one you are absolutely positive is real, then wake up, and realize its not. I think I've had this dream before, that I had an "extra" room in my apt, which I didn't use. And living in a small 1BR apt, that's a big deal! So in my dream, I was trying to figure out how to use it/what to put in it. I know there's some strange parallel to real life, but can't figure out what it is.
Anyway, I woke up, and for a second was all excited, WOW, extra space, then slowly came back to reality and realized, no, just a dream.