What you described is definitely how I feel when I really get into the zone of something, whether it be coding something very specific or doing overall design/architecture.

As I get into it, it suddenly snaps into place, and I have a mental picture (which is more visceral than visual) of how all the moving pieces fit (or will fit) together, and can start adding on to it. With coding in particualr, usually my brain is going faster than my ability to type.

I absolutely love that feeling.