There is always those "other" worlds, even within one's own head. One can't react/respond to "nothing"? There'd be a void if there was nothing out there, being manic would have no meaning.

Living in your head, you are still making up other worlds in there and, for me, they caused most of my problems, not the outside world. The outside world is the same problem for everyone but the inside one is different/changeable based only on ourselves. It's the inside world that is treacherous.