What causes you to have deja vu?

just coincidence, but i definitly identify. u mite hav been thru so much that it just feels like deja vu

There are several possible explanations for what is occurring during a déjà vu experience. One possibility is simply the occasional mismatch made by the brain in its continuous attempt to create whole sensical pictures out of very small pieces of information. Looking at memory as a hologram, only bits of sensory information are needed for the brain to reconstruct entire three-dimensional images. When the brain receives a small sensory input (a sight, a smell, a sound) that is strikingly similar to such a detail experienced in the past, the entire memory image is brought forward. The brain has taken the past to be the present by virtue of one tiny bit of sensory information. It is this mismatch of past and present sensory information that causes the sense of disconcertment and unease associated with a passing déjà vu .This theory provides a satisfactory explanation for the physical effects of déjà vu. These appear to be similar to the effects of mismatch between sensory input and corollary discharge signal information to the brain. It does not, however, seem to provide sufficient answers to individual (even my own) accounts of déjà vu, where the memory image pulled up is not necessarily from a true past event.

gdev is right :)