Near-death experiences (NDE) are lucid events that take place when a person is so physically compromised that he would die if its condition does not improve. He is unconscious, without heartbeats and breath, and with a flat-line electroencephalogram. NDE may include some of the following elements: Out of the body experiences or separation of consciousness from the physical body, increase in sensory perception and intense emotions, travel into or through a tunnel, encounter with a brilliant light and mystical beings, deceased relatives or friends, a sense of alteration in time and space, visualization of unworldly realms and a special knowledge, encounter with a barrier or boundary, and a return to the body, either voluntary or involuntary. The fact that children NDE are similar to adult NDE is an evidence that these experiences are real and not due to pre-existing beliefs, cultural influences or previous experiences in the present life. The characteristics of NDE are similar worldwide. No evidence supports the physiological, psychological, neurochemical, and neuroanatomical hypothesis proposed to explain the NDE. Multifactorial models, based on the combination of all of them (brain anoxia or hypoxia, release of serotonin,endorphins and ketamine-like compounds) have also been proposed. Although physiological, psychological, and socio-cultural factors could interact in the NDE, the hypothesis proposed consist essentially in unsupported speculations about what might be happening during the NDE.
