2474...
I don't know what causes it, pretty sure it's not dreams though, I'm very good at remembering dreams (but I have to say sometimes i have like 5 different dreams at one night and sometimes only 1 or 2, soo that means I could have easily forget some of them anyway XD )
Maybe it's just that it's something similair that you've once seen or done but then in another form or shape or whatever...
Oh wait i DO remember this one dream that came out, with just some slight changes as location, but what happened was the same, was very weird, but it didnt really feel like a REAL dejavu feeling. just like oh man I dreamed of this XD
Oh well, we'll never get rid of deja-vu feelings ^^ and I don't care if I dunno what caused them, most of the time they only last a few seconds anyway