I’m convinced deja vu is previous dreams coming to form. When you get deja vu, feels a lot like a flash rememberance of a dream yea? Some instances that played out were so extremely familiar I’m convinced they happened in my brain at some point in time.
I don’t think that the future is set in stone. When we catch a glimpse of it in a dream, that is simply one possibility that may occur. The outcome of any event is only decided in the present.
That having been said, I have had some unusually strong deja vus lately. I not only get the strong feeling of having “done this and been here” before, but I sometimes know what’s about to happen. So far, this only happens with random events. I’ll get a sense of deja vu, stop, and then know exactly who is about to walk up behind me and what they’re going to say.
My most coincidental (if coincidence it was) dream coming true occurred a few years ago. There was this girl who I’d had a crush on for some time, and she didn’t know about it. One night, I dreamt that we were kissing. Being a good dream, when I woke up, I wrote down the day and time: 10 Oct 1996, 2:36 am. Well, quite a while later, she and I started dating. And on 10 Oct 1997, we had our first kiss. And most amazingly, it happened sometime between 2 and 3am! I don’t know the exact minute. When I was browsing my dream journal a few days later, I discovered what had happened and was speechless.
I also had a dream in which my great aunt died. I wrote down the day and time; exactly two months later, at exactly the same time (6:17am), she passed away. I don’t know what to make of any of this. I tend to be skeptical about most things, but these are rather odd coincidences. 
Don’t you hate it when this happens and no one believes it when you tell them? It makes me so mad because there’s no way to prove it to them! 