hm.

i'm thinking it's a memory thing. I can't find the link right now, but there's an article on a relatively new theory of how the brain creates memories called "Holonomic Brain Theory". It's based on the idea that as you are developing a memory of a particular event (like riding your bike at the moment), your brain thinks "bike, street, weather, houses" whatever you're taking in around you. So memories are only a junction of these ideas, to trivialize it.

It follows that de ja vu may be when your brain retraces a junction to create a new memory because the ideas that compose it are so similar to an old one that it accidentally "overwrites" part of it. So as an event is happening (like riding your bike down a street someplace you've never been) you think it's somehow familiar to you, but it's not. It's just that you can't remember what was there before because it simply isn't there, what's happening now is there instead.

So maybe dreams, or memories of dreams can follow this pattern as well. Maybe when I'm somewhere new (because that's where new memories are bound to be forming more than a new memory of the street i live on) my brain is replacing something from a dream (for whatever reason).