Would you like to go into a sensory deprivation tank?
With a complete lack of any sensory stimulus, you soon begin to naturally hallucinate. Your brain is so used to constant calculations - such as in the extraordinary complex mathematics involved in spacial awareness that we are not aware of - that in the absence of any dimensions, sights and sounds it creates its own hallucinatory stimulus to keep ticking over.
I asked this in R&S because some people come out with a new understanding of life, and their material bodies.
Here is a guy talking about his (trippy) experience: