Thats one of the typical neurone miss fires which is used to dismiss it as just "something the brain does" like a mistake but if our brains made that many mistakes it could quite easily damage itself.

I play bass guitar and electric guitar and its quite easy to tell you that if i stopped and thought about everything i did i wouldn't get one second of a song out. Like if you stopped to think about driving a car you would crash straight away. The brain has a subconcious seemingly to keep your "concious" (of what we see) doing the important things that need more controled thought on.
What im thinking is that neurone "miss fire" is sometimes the cause but it happens to regularly and is too common for me to accept that its just my brain making a mistake. That essentialy everyone in the whole world has a mental disorder of a major degree is somewhat unnerving.

My DeJa Vu experiances some are just the wow thats odd ones but others like i said i can remember seeing them in a dream which i've just forgotten about over a couple of hours or days but our brain doesn't "forget" it just puts it in the "back of the cupboard" (so to speak) so that our brain doesn't get clogged down. So the my brain "missfiring" is either effecting the past (which i've written my dreams down before and had the deja vu of it weeks or months later) or it is something slightly bigger.