Deja Vu and Dreaming

According to Websters New World Dictionary: deja vu - (n) a feeling that one has had an experience before, although the experience is actually new.

Deja vu: French for already considering or already seen.

  Recently a friend posed the question, "What is actually happening when we experience deja vu? Are our lives actually deeply predestined?"
  One person answered, "Neurological short circuit. Our brains are similar to our computers. We have short term easy access memory, and then at the end of the day, when we dream, we process the days data into long term memory. A "deja vu" is when a short term memory (what just happened a moment ago) is immediately written into long term memory and when retrieved a moment later it feels like it happened ages ago and was pre-seen."
  Another had said that they had been told , "deja vu is a sign that you are on the right path."
  Both interesting replies.

  Sigmund Freud believed the feeling corresponded to the memory of an unconscious daydream.
  Freud in a partial summary of authors who had discussed the issue, separated them into "believers" (who thought that deja vu was proof of a previous existence.), and "non believers", who regard such events as false memories. Freud himself assumes a different position, by believing in the reality of the representative content but associated this with the reactivation of an older unconscious impression.
[ answer.com - S. Mijolla-Mellor]

  Fulfillment of a prior premonition of a forthcoming event.
  According to Arthur and Joyce Berger " The Encyclopedia of Parapsychology and Psychical Research", (It's) connected to experiences of reincarnation when a feeling of prior knowledge is so strong that people feel it must come from a former incarnation. The case of a young girl, Shanti Devi, born in Delhi, India in 1926. She had claimed to live elsewhere in a former life and had gone on to be taken to this place where she identified places, the house, family, and other circumstantial details. There have been other similar circumstances over the years.

  Deja vu and dreaming seem to come together quite often. My own personal experience with a dream precognition had nothing to do with me and has always upset me due to the circumstances so I have only mentioned it once to one other person. The dream was a recurring one ( I had had it 2 or 3 times). I was walking through the streets of a large city of glass buildings, everything was in black and white like an old film from the 40's. I was dressed in the style of that era, as was everyone else (all hats and ties, business dresses and silk stockings). I heard the sound of a large airplane and looked up to see it flying low between the giant glass skyscrapers. The plane slams into a building with  the loud sound of shattering glass. Giant pieces and glass dust falling everywhere. People running and screaming. I just keep staring up at the scene. Many, many months after I had had the dreams (all of which seemed identical to me) the unfathomable happened and causing me my deja vu and causing a war which we still fight. Now you know why I kept my mouth shut about this dream.