Deja vu'

What exactly is this experience of Deja vu? I didn't know that it could actually exist till i found out, years ago, that it had a name. Unless experiences are given names or people share the totality of their fears with others, it w'd seem a burden to unleash them on others.
I think Deja vu occurs in stages...the first being of a vague unease, followed by patterns falling in place, quickly, and then these new elements seem oddly familiar and a wave of relief surges past oneself.
Sometimes the experience itself is protracted, for what seems like ages and then it quickly dissipates. At other times, the light and shade of it is mixed all in shadows and one finds it hard to differentiate one from the other.
Scientific explanations range from the dark to the unclear. It is considered to be the aura of an epileptic process or the precursor of one. It may also be part of an altered state of consciousness, a kind of a detachment from oneself and this world. It could herald unhappy things in the brain, commonly called tumours.
Deja vu means a state of experiencing new happenings as if they had already happened. Who knows why it happens unless it is a reminder of us not forgetting that the past and future are a mixed bag of things and that in one is a reflected mirror of the other. I struggle to find anything poetic about it apart from the mystic solitude it brings. There is a remoteness, a deep unease about it and in this all is a silent lesson.