Based on my experiences, when one experiences a Deja Vu, one is simply reminded, consciously or unconsciously, that she/he is playing along the lines of the planned life he/she has set up before coming into this world.
These are reminders, consciously or subconsciously, depending on one's consciousness, left by us before coming into this world, like "hellos" from the other side, from ourselves to ourselves.
I experienced two major Deja Vu lately, really strong ones, yesterday and today and it was incredible!!! I started laughing out loud uncontrollably experiencing pure joy