The unique experience of human consciousness comes of a brain that maps the body of which it is a part with sufficient complexity and nuance. The circumstances that produce such a brain are complicated and a little improbable, but ultimately finite and scientifically ordinary. As consciousness is the definitive state of existence, we can only know ourselves to exist as we know ourselves in any moment. To lack this consciousness would mean being, from the perspective of any other particular individual we might have in mind, nonexistent.