Near-death experiences, or NDE's, from the Psychology definition refers to a broad range of personal experiences associated with impending death, encompassing multiple possible sensations ranging from detachment from the body, feelings of levitation, extreme fear, total serenity, security, or warmth, the experience of absolute dissolution, and the presence of a light, which some people interpret as a deity.
Some see NDEs as a paranormal and spiritual glimpse into the afterlife.
Such cases are usually reported after an individual has been pronounced clinically dead, or otherwise very close to death, hence the entitlement near-death experience.
Many NDE reports, however, originate from events that are not life threatening. With recent developments in cardiac resuscitation techniques, the number of NDEs reported has increased. Most of the scientific community regards such experiences as hallucinatory while paranormal specialists and some mainstream scientists claim them to be evidence of an afterlife.
Popular interest in near-death experiences was initially sparked by Raymond Moody, Jr's 1975 book "Life After Life" and the founding of the International Association for Near-Death Studies (IANDS) in 1978. According to a Gallup poll, approximately eight million Americans claim to have had a near-death experience.
NDEs are among the phenomena studied in the fields of parapsychology, psychology, psychiatry, and hospital medicine.
(This reply intended as an informational but not definitive guide based on current scientific theories).