Interesting question! I don't know if I've ever woken up in the middle of the night and started thinking of a current build but I DO know that I've drifted off to sleep with the wonderful thoughts of my current model swimming in my head. I think of what step I'm on now and what steps I'll be taking next.
I've found it to be a very relaxing way to let go of the stress of the day and a great "last waking thoughts" of the day.
Eric