I'm perusing a book on shamanism entitled "Dreamtime and Inner Space", by Kalwett. I came across this paragraph which I'm sure you will find has obvious parallels to a certain experience we all share:
"Before the consciousness of a dying person separates from the body, that person often hears a curious noise, described as a cracking, clicking, or rushing sound, but sometimes also as wonderfully harmonious. A twenty-eight-year-old man, who attempted suicide in prison, reported that almost immediately he heard curious sounds: "(I) heard all this ringing, this loud, loud ringing, and then a black hole and all these luminous things around and beautiful music, the most beautiful music I had ever heard. The ringing came from a low to a peak, which faded into choral music which was all around me. It was the most beautiful experience I think I've ever had, just totally encompassed in sound, the most beautiful voices I'd ever heard...
"After the clicking sounds (or heavenly music) and the subsequent separation from the body, people feel themselves drawn into a dark tunnel or space like a cave or hole. A twenty-five-year-old man, who was revived after a suicide attempt, said that he suddenly lost the feeling that he had a body. He felt like energy in the universe. There was total darkness and he was rushing along at enormous speed toward something pitch black. He was being sucked toward it, or drawn toward it."
Sounds like some serious endogenous DMT production to me...
"...I didn't know that Cheshire cats always grinned; in fact, I didn't know that cats could grin..." - Alice's Adventures in Wonderland