Near-Death Experiences (NDEs) are a remarkably common experience among people who have nearly died and been resuscitated. There are a variety of symptoms associated with an NDE, including but not limited to:

The notice of a very unpleasant sound or noise.

A sense/awareness of being dead.

A sense of peace, well-being and painlessness. Positive emotions. A feeling of being removed from the world.

An out-of-body experience. A perception of one’s body from an outside position. Sometimes observing doctors and nurses performing medical resuscitation efforts.

A "tunnel experience". A sense of moving up, or through, a passageway or staircase.

A rapid movement toward and/or sudden immersion in a powerful light. Communication with the light.

An intense feeling of unconditional love.

Encountering "Beings of Light", "Beings dressed in white", or other spiritual beings. Also, the possibility of being reunited with deceased loved ones.

Being given a life review.

Being presented with knowledge about one's life and the nature of the universe.

A decision by oneself or others to return to one’s body, often accompanied by a reluctance to return.

Approaching a border.

Not all people experiencing an NDE will experience all of the above, and there are a wide range of other unworldly experiences that may occur during an NDE. Approximately 60% of those will have an out-of-body experience, but only 10% reach the stage of joining with or psychically communicating with a light. There are some cultural variations among the visions. Some people, particularly children, often find themselves communicating with people who are alive (such as classmates). NDEs are more often pleasant, but occasionally terrifying. Patients who felt that they had to return typically reported the reason as being that they had to tell people about what they saw. The observations of doctors are often quite real and accurate, involving specific details despite the patient being unresponsive and seemingly unconscious.

Above: A young girl who nearly died of bacterial meningitis draws her experience. A doctor involved described the recreation of the operating room, including the positioning of individuals and their arms, as spot-on.

The overall experience of an NDE varies from negative to positive. One survivor explains:

Yvonne Malik felt that she had to pass through 'humanity's fear and ignorance' during her NDE, and that in the end she was 'allowed' to return because she wanted to show others that life after death does exist: I seemed to be in some outside place which was dark, or almost black, and I was going towards an even blacker area. I wasn't running but was moving; aiming to go up the side of a black mountain; in the dark going upwards. Although it was so dark, I could 'see' that I was passing or being passed by a lot of men and women who were all rushing in the opposite direction away from me. They were telling me in both an apathetic and angry way, not to go in the direction I was going because there was nothing there, that I was a fool, that it was useless and led nowhere. Suddenly it was as if I were up on top of the mountain on a kind of plateau, it wasn't cold and there was no wind. I could see the tops of other mountain ranges and valleys, but was too high up to see people. I was surrounded by light, it was golden yellow, very bright and seemed to become brighter and whiter. There was no need to squint as it was not painful. Words are only useful when used to describe parallels - in this case words do not seem to work. The light itself had a personality, it was joy (an old-fashioned word). The air itself seemed to be full of love and joy. Although I did not look around, I felt strongly aware that two 'guardians' were standing just behind me on my left. It seemed to be that I should not turn around to see them, but as I felt so sure of their presence, it did not seem important to try to do so. I had the definite feeling also, that they had great wisdom and compassion. They seemed to 'tell' me that I could stay there in this absolutely wonderful place/experience if I wished. I do not know why on earth I said, No, and that I must go back to tell others just how wonderful it was and that it was untrue that there was nothing beyond the dark.

Naturally, one hypothesis to explain such NDEs is that one is briefly encountering the afterlife. This would explain the remarkably common elements and the frequency of NDEs themselves, as well as the observation of events outside their body. However, this hypothesis does not as readily explain a variety of other elements, such as the cultural differences in NDE experiences, communication with living individuals during an NDE, the difference in NDE experiences between children and adults, the wide range of "other" unworldly experiences (such as the above stream of people heading down the mountain), and a variety of other phenomena.

There have been several medical hypotheses relating to NDEs proposed throughout the years. For example, it has been observed that people who have difficulty separating the real world and their dreams and those who have REM when not asleep are much more likely to have an NDE, providing some evidence that the two phenomena may be related. However, this diary will focus on the remarkable similarity between the NDE experience and that of users of the drug ketamine.

Ketamine (Medical names: Ketanest, Ketaset, Ketalar; Street names: K, Ket, Special K, Vitamin K) is a member of a class of drugs known as "NMDA receptor agonists". It is structurally similar to PCP, but generally considered much safer (even possessing properties that help prevent neuron damage). As the dosage increases, ketamine begins binding to a wider range of receptors, including opioid μ receptors and sigma receptors, some of which decrease its bioavailability and help prevent overdose. This built-in safeguard has made it a popular anesthetic; however, due to the severe hallucinations it can cause, it is generally only used with other anesthetics to help ensure complete unconsciousness.

As a street drug, ketamine is used precisely for said hallucinations. The experience of being on ketamine is very different from that of LSD, which binds to entirely different receptors (the "G-protein coupled receptors"). The effects of Ketamine have been well studied. For example, in a Russian experiment with alcoholics:

Thus the enhanced spirituality in patients after KPT might be an important element to the therapeutic action. Regarding spiritual experiences induced by ketamine, it is interesting that many people who never thought about spirituality or the meaning of life reported having profound religious transformative experiences. At the ketamine session, people often experienced the separation of consciousness from the body and the dissolving of the body ego. For many patients, it is a profound insight that they can exist without their bodies as pure consciousness or pure spirit. Some of them said that as a result of their experience, they understood the Christian notion of the separation of the soul and the body. Some people reported contact with God, and after coming back to ordinary consciousness, they feel sure that they have had contact with a higher power. Many patients reported the existence of other dimensions or other worlds that are parallel to ours and seem as real or even more real than our own. Some patients experienced the expansion of consciousness to encompass the whole universe, whole cosmos, etc. They often said: "I ceased to exist, I disappeared, yet still just my consciousness existed. It was like I became the whole universe or the whole cosmos".

Users of Ketamine frequently display little responsiveness while fully experiencing the world around them through the prism of a disassociative hallucination. They sometimes refer to the experience as being like an NDE:

I’ve heard about ‘Near Death Experiences on Ketamine? What’s up with that? Near-Death and Near-Birth Experiences A 'near-death experience' (NDE) is a report of leaving the physical body, and sometimes going through a tunnel towards 'the light'. Ketamine can reproduce all aspects of the NDE, including the conviction of being dead, having a telepathic communion with God, seeing visions, out-of-body trips, mystical states, entering other realities, re-experiencing old memories, and a life review which may have therapeutic value Most NDE's occur in people who are not physically near death.

While the experiences are not a perfect match and are not universal, they are remarkably close in some cases. This curious connection between the effects of ketamine and the experiences of patients who are undergoing severe neural hypoxia calls for an explanation.

The immediate hypothesis -- that perhaps ketamine itself, administered as an anesthetic, causes all or nearly all NDEs -- is readily disproven. Ketamine is not frequently used in such circumstances and is not present in most cases of NDEs. However, an interesting possibility presents itself in the primary receptor that ketamine activates in causing its hallucinations: NMDA.

Ketamine owes its neuron-protective abilities to its ability to prevent excitotoxicity. That is, under conditions of hypoxia, glutamate (the primary neurotransmitter in the cerebral cortex) is released in excess, killing neurons. Blockade of the NMDA receptor has been shown to reduce or eliminate this effect. Hence, under conditions of hypoxia, any activity of NMDA receptors by the brain would serve as a defense mechanism.

Does the brain have such a defense mechanism? At this time, it is unknown, although there are a number of hypotheses on the subject. For now, there is no conclusive proof as to what phenomena cause near-death experiences.