I've just stumbled across a massive cache of memories that were, in fact, dreams.
I spent last night wandering down the streets of a place I used to live, only to wake up and realise that nothing I had dreamt in any way resembled the real city as I remembered it.  So I started digging.
As soon as I try to place any of these memories geographically or chronologically, I come up with a blank.  As far as I can tell, I've dreamt up an entire city.  I have taken trains there, across a river on a huge elevated track.  I've spent ages in one of the stations, trying to transfer lines.  I've wandered around two different shopping malls, and a string of charity shops.  I've trekked miles trying to find the right bus into the city, and then back home, which required travelling around a lake.  Most disconcerting of all, I've gone to school there.  I don't remember why I visited the high school.  I think I was taking a night class.  I just remember it being massive and labyrinthine.  The university is even more so.  I distinctly remember two different residence buildings.  I had a fall and winter schedule.  I have memories of weeks and weeks worth of classes.  I can picture the classrooms, and all the hallways leading to them, and I know they do not exist.  None of this ever happened.
Which begs the question: how many of my other memories are actually dreams?