I am not sure if we are all experiencing the same thing here,because i have never had what the last two posters described,and if i did i wouldn't call that deja vu cuz deja vu feels totally different to me. It doesn't have anything to do with visions or seeing things. I dont know,unless there is more than one kind of deja vu. I've only had the kind where whatever you're doing,it feels like you know whats gonna happen as it's happening. Like for about 5 seconds,you can see the future a second ahead of time.
I have had wierd visions and flashes of people i dont know (who probably dont exist) but they always happen as i'm laying in bed falling asleep. I get lots of strange visions then,of scenes and people. But they are quick flashes and dont mean anything to me and they never fit in with my dreams or anything else in my life. I just figure those are results of your brain falling asleep,misfiring. Kinda like how some people say when you die,your brain is going through wierd stuff so you'll see and hear wierd things that mean nothing.