Joscha Bach says the sense of realness is represented in the mind: dreams can make ideas feel real, while sensory-validated perceptions of the outside world are tagged as real by the brain.

“It's a representation inside of my own mind. And when you dream, you often dream that ideas become real. And when you perceive the, uh, outside world, then all the stuff that is validated by your sensory system is tagged by your brain as real.”