The effects of DMT and 'trip reports' correlate almost exactly to what NDE (Near Death Experience) accounts describe. In ancient times, what some would call prophets would stay in totally dark rooms for several hundred hours...
One of the criticisms made against supposed near-death experiences is that often the subject was actually in no danger of dying, so it wasn't "near death." But that kind of misses the point, in light of the similarities often reported between the experiences of psychedelic drugs (see also Aldous Huxley's
The Doors of Perception, an account of his experience on mescaline), NDE's, sensory deprivation and deep meditation. You haven't mentioned meditation, and you suggest several hundred hours as a threshold for sensory deprivation, but many people have reported 'hallucinatory' experiences similar to a psychedelic trip after even
as little as fifteen minutes of sensory deprivation.
Seems to me that a plausible common thread between each of these types of experience is the potential for a willing or induced
dissociation of the mind from the body, whether through the mental discipline of meditation, the feeling (even if later found to be factually inaccurate) of being 'near death' and so on.
Of course an alternative guess as to the reason for experiences like these, particularly psychedelic trips and NDEs, is that the brain itself generates the 'hallucinations.' It doesn't seem very obvious why that would be the case for sensory deprivation, and even less so for meditation, but there's at least one particularly intriguing case of a documented NDE, that of
Pam Reynalds, for which a complete absence of brain activity was recorded:
As a last resort, Robert F. Spetzler, a neurosurgeon of the Barrow Neurological Institute in Phoenix, Arizona, decided that a rarely performed procedure, known as hypothermic cardiac arrest, could improve Reynolds's chances of surviving surgical removal of the aneurysm. During this procedure, also known as a standstill operation, Reynolds's body temperature was lowered to 50 °F (10 °C), her breathing and heartbeat stopped, and the blood drained from her head. Her eyes were closed with tape and small ear plugs with speakers were placed in her ears. These speakers emitted audible clicks which were used to check the function of the brain stem to ensure that she had a flat EEG—indicating a non-responsive brain—before the operation proceeded. The operation was a success and Reynolds recovered completely. The total surgery lasted about seven hours with a few complications along the way.[4]
Reynolds reported that during the operation she heard a sound like a natural 'D' that seemed to pull her out of her body and allowed her to "float" above the operating room and watch the doctors perform the operation. Reynolds claims that during this time she felt "more aware than normal" and her vision was more focused and clearer than normal vision. She reported seeing the surgical "saw" but said it looked like an electric toothbrush, and this is in fact true. She said she could hear conversations between operating room staff, even though she had earphones in her ears which were making a loud clicking noise many times per second in order to monitor her brain function. At some point during the operation, she says she noticed a presence and was pulled towards a light. . . .
There are
ad hoc 'explanations' for Pam's experience too, of course; maybe she had anaesthesia awareness and a lucky guess about the saw during that part of the operation, and despite her reports maybe the hallucination didn't extend through the period for which she had no brain activity. The fact is that we can't really be sure one way or the other; but so-called 'sceptics' are often hyper-sceptical in only one direction, only against things which might conflict with their pseudo-scientific reductionism, and re-cast these guesses about alternative explanations for experiences like Pam's as constituting a thorough 'debunking' leaving them with zero evidentiary value.
Personally I would say that the
ad hoc alternative doesn't seem any more convincing to me than Pam's own account and interpretation of her experience, implying that even Pam's account alone (to say nothing of the wide range of credible similar reports) would suggest something like a 50/50 plausibility for the proposition that consciousness can persist and even increase in vividness beyond the cessation of brain function.