Long ago I invented a way of explaining how the feeling of deja vu could be explained.

In essence, the feeling is that of experiencing something in the present and yet feeling a weird sense that it has happened before - that it is a memory rather than just a current event.

My idea was that when information is recalled from memory, it is "tagged" somehow to indicate that it is a memory and not happening right now. Memories can be very vivid, though they certainly are not usually confused with reality. Information passing to our conscious self from the senses may or may not be tagged to indicate its type.

I think when we experience deja vu that the "memory tag" accidentally gets released (it would be some sort of chemical reaction of course) while we are currently processing sensory information. So while we know we are looking at the thing now, we also get this mixed up signal that what we are considering is a memory.