Well, it is like a normal dream which is much like reality in the sense that you walk around and experience things like you do normally, these experiences are created by your brain from pure memory and expectations and feel extremely real.
But when you become lucid YOU can decide what to do and what to experience.

So it is like living in another reality for a limited time each time you become lucid. It's not like you are "imagining" it, if that's what you mean.