I say this only partly humorously. They need to do a wide variety of mind-bending drugs to experience what the brain is capable of; there is no part of you that can't be manipulated to simulate these things. Those experiences are, most likely, manifestations of physiological stress; oxygen depletion, for one, can give you 'floaty' out of the body experiences. If you think about the process of gradual oxygen depletion to the body, the brain gets highest priority and, as a result, imagine what it would be like to be awake but lose all your tactile body senses first. You will feel like you are floating because your brain no longer receives the information from those parts because any oxygen left is increasingly prioritised for the brain.
The next step in the process will be diminishing vision, which becomes tunnel-like as you lose peripheral vision first. This is the 'light at the end of the tunnel' effect many people apparently have who said they had a near death experience. I read a step-by-step analysis many years of the process of dying and the gradual termination of physiological processes which adequately explains these apparently paranormal experiences