James M. Tabor on supercaves - the deepest, baddest caves on Earth. Talking about the physiological effects, he notes:
"Another thing is that each human brain has a unique tolerance for darkness. Some individuals reach their limit after a certain number of days or certain number of feet below the surface, and then they have an attack called The Rapture, which is like a panic attack on speed. I’ve interviewed people who’ve experienced it and they say it’s like a panic attack but multiplied a hundred times in intensity..."