Why does deja-vu happen?... (ha ha)... I heard an idea that it was due to the fact that our conscious mind is lagging behind the real world. We already know that the reflexive side of the brain is much faster than the thinking part. This is the explanation that seemed to be most in tune with what I understand, but there are many other ideas as well!

You also see doppelgangers! I only catch them out the corner of my eye... People that look so familiar... or somehow similar to people I know, but that are not actually that person! I guess you could ask them, if you could ever catch one without looking like a crazy nut!