This is also something Tesla would do! - "But instinct is something which transcends knowledge. We have, undoubtedly, certain finer fibers that enable us to perceive truths when logical deduction, or any other willful effort of the brain, is futile."
Taking off parts and swapping out others.
It was really nice learning CAD design for this reason...being able to properly get the designs into the real world.
Do you remember a time before you visualized effectively? (Is it something practiced?)
I don't recall any time where I couldn't visualize. I can remember back to when I was 3-4 fairly well and I always remember this being part of how I am.
For the most part I remember everything I read also...which can be bad since at times misinformation that has also been memorized makes me second guess.
As far as designing in my sleep...I mainly just focus on the problem as I am falling asleep. I find that when I wake typically there will be progress on the design which I can go mechanically work on. This is mostly during the assembly phase that I use this though...when I am actually assembling the machine and debugging the last minute "gotchas".