This is an interesting subject, I have in one of my books how someone felt she had Deja-Vu at a restaurant. She just had this weird feeling like she had been here before and done all of this before. She was at a restaurant and the lights went out, a waiter with shinny buttons brought candles over and they had to sit and eat by candle light. She wrote this experience down in her journal and decided to look through it to see if she could find anything in the past similar. She found the entire story she had dreamed years ago, every detail perfect, the only thing wrong with the dream was she was with a man she had no idea who he was, and in life it was her husband whom she did not know when she dreamed the event.

Another I saw on television was a women that swore she felt like she had been to Ireland before, everything was so familiar. She not only felt this as she explored more about Ireland she felt she had children that she lost there! She went into hypnosis and found in a past life she lived there, and had this name and these three children. After that she started really researching and found these children that were now old she flew over to them and got the family back together and they all swear it is their mom came back for them even though she is much younger than they are.

I have been watching a movie already that I never saw before and felt like I did see it and could tell what was going to happen. Science says that is an epileptic seizure it could be I have no idea, or maybe I dreamed it but there has to be something bigger if all time and space is now then what seems like future is now and what seems like past is now then it makes sense that the brain could "go out of tune" "epileptic seizure" and experience the future now as the present or the present as the past.

It is something to ponder on though.

Another option is that we are shown this life, before coming here. Not in exact detail, of course, because our own free will and the free will of others will change some things, but we are shown signposts and a general view of the life we will have here on this plane. Some believe we then decide to accept the life, or ask for something else. So it could be true that something happens along the way, that we recognize on some level from seeing it before, and for just a moment, we remember that we've seen it already. Once that was explained to me, I was no longer mystified when I feel deja-vu.

Wikipedia has a good article on the topic that you may find informative. The most likely explanation, it says, "is not that it is an act of 'precognition' or 'prophecy', but rather that it is an anomaly of memory giving the impression that an experience is 'being recalled' ". Read the full article. It makes a lot of sense.

I've had many déjà vu experiences but none of them have brought any significant insights to me. However, there is a sense of familiarity and comfort to them when it happens and I take that as a confirmation of sorts that I am where I should be, doing what I should be doing.

Another explaination is .. Dreams. most of the time we can't consciously remember our dreams. but we can have a very strong feeling whe we experience in reality what we expereinced in a dream. this is how our subconscious tell us ''I told you so''. sometimes, it's not only a strong feeling. sometimes we remember the dream as a vison. we remember every part of it at the same moment of experiencing it in reality. this creates mental confusion. because the conscious and subconscious are like talking to you at the same time, and saying the same thing.

The nerve pattern’s activity causes the illusion of a present, in which your consciousness appears focused and alert. In certain terms "future” events exists now, but they are too fast. They jump over the nerve endings too quickly, and physically you cannot perceive or experience them as yet. Beneath your usual consciousness, your physical organism can react to future events without your knowledge, as it can to past ones. In such cases the intensity of the initially nonphysical event is enough to break through normal neuronal patterns.

If you are aware of such a future episode, you will be forced to react to it as a conscious being. In any case your temporal structure will respond whether or not you are aware of the reasons for such behavior. The future incident may then occur in its time sequence, and you recognize it through memory, in which case your reactions in that future present will be altered because of the seemingly past memory.

Source: The nature of personal reality