I have actually met people who vehemently insist that when they "space out" they aren't deep in thought, they are literally off -- not thinking at all.
It's pretty astonishing how much variation there is in people's inner minds. Some can imagine spatial relationships in great detail. Some can't even imagine a simple stick figure, but can instead remember long lists of information.
You still can't just "turn off" your mind, most likely. You'll just be trapped there thinking