the power of the human mind

I left class thursday a little disturbed, it seemed to me that a lot of people didn't have a lot of faith in the human mind's strength and it's ability to think. The question was "Does a human being suspended in air with no senses know it exists?" There was a lot of discussion leaning in the direction of saying it wouldn't which was surprising to me. Regardless, it got me thinking in large part about what the mind would be doing over long periods of essentially darkness and surrendering to a state of not feeling. We as humans, surrender our senses out of will for meditation in different ways, but I think the closest to complete unkowningness is a coma patient. What does the mind create in those dark periods of time? I think it would be something rather horrific, a second world filled with nightmares. If the brain isn't getting reference from things that exist the abstract forms it would create I think would be horrific in nature.