A surge of steroids, epinephrine, and adrenaline are released in the body during situations where it's near death, Parnia points out. It could explain the feeling of euphoria, and some of the stranger, hallucinatory effects. It's been suggested that Ketamine, which is released when animals are under attack, could produce similar effects. One of the first theories on near-death experiences, in fact, was that the psychedelic Dimethyltryptamine, or DMT, was released in the brain as soon as it realized it was dying, but that's somewhat speculative: The only way to really test something like that, Nelson says, is to give someone the drug and compare its effects to near-death experiences. Chemicals could very well be be a factor; it's just not an easily proven one, compared to, say, fainting and blood loss.