Near-death experiences are profound events that often radically change the lives of those who have them. 

Features of near-death experiences include a sense of leaving the physical body, a life review, and encounters with a divine being or deceased loved ones. 

While some dismiss near-death experiences as dreams or the hallucinations of a dying brain, people generally do not have the same kinds of hallucinations. In contrast, the descriptions of near-death experiences are remarkably consistent across culture and time.

DR. BRUCE GREYSON: Near-death experiences are profound, subjective experiences that many people have when they come close to death or sometimes when they are, in fact, pronounced dead. And they include such difficult to explain phenomena as: a sense of leaving the physical body, reviewing one's entire life, encountering some other entities that aren't physically present that they sometimes interpret as deities or deceased loved ones. And at some point coming to a point of no return beyond which they can't continue and still come back to life. 

It's natural for people to think that near-death experiences are kind of like dreams or hallucinations. No two people have the same type of hallucination. Whereas near-death experiences are basically the same across people, across cultures, across centuries. I think if you look at what things typically cause hallucinations- metabolic changes, drugs, changes in oxygen level, brain injury, those things produce certain known effects: confusion, agitation, belligerence. They're very different from the typical calm, peaceful, consistent content of a near-death experience. We've looked at specific things that may cause a hallucination. It was thought that maybe lack of oxygen to the brain would have a role in near-death experiences, since no matter how you come close to death, lack of oxygen to the brain is one of the final, common pathways. But those who report near-death experiences actually have better oxygen flow to the brain than people who don't report NDEs. 

Likewise, we thought drugs given to people as they approach death may be causing these experiences. And what we find again is that the more drugs people are given as they approach death, the less likely they are to report a near-death experience. So drugs and lack of oxygen are not causing NDEs. They may in fact, repress having an NDE. 

You can look on a dream as just a random series of visions; a way of processing problems in your life, and finding solutions. There are phenomenological differences, differences in the content between dreams and near-death experiences. Near-death experiences often have accurate out of body perceptions, whereas dreams and hallucinations do not. And that to me is probably one of the best ways of distinguishing between a dream and a near-death experience. Is there any connection between dreams and near-death experiences? The fact that both of those are processed by our brains ultimately says that there's got to be some similarities in how we describe them, how we understand them, how we relate them to other people. 

Many near-death experiencers report things that other people can't verify right away. So we assume that they were just imagination or fantasy, and yet they insist, "It's real. It's happened to me. I know it." Philosopher Abraham Kaplan talks about the story of a traveler who went to a distant land, and came back with a fantastic story about a beast who can travel for days and days and days without water. And he tells this to his people in his town and they get together and say "We don't know if this can be real, but we're gonna get the wise men together and have a meeting and decide whether this beast can exist or not." And the traveler says, "What do you mean can exist? I saw it." So it's like, if you were hit by a truck, and someone says you just imagined it. You know whether you're hit by a truck or not. There's no doubt in your mind. And that's the way near-death experiencers relate to their NDE. They feel like, 'There's no doubt in my mind, this is a real experience I had. More real than this world is.'