An out-of-body experience (OBE or sometimes OOBE) is a phenomenon in which a person perceives the world from a location outside their physical body. An OBE is a form of autoscopy (literally "seeing self"), although this term is more commonly used to refer to the pathological condition of seeing a second self, or doppelgänger.
The term out-of-body experience was introduced in 1943 by G. N. M. Tyrrell in his book Apparitions, and was adopted by researchers such as Celia Green, and Robert Monroe, as an alternative to belief-centric labels such as "astral projection" or "spirit walking". OBEs can be induced by traumatic brain injuries, sensory deprivation, near-death experiences, dissociative and psychedelic drugs, dehydration, sleep disorders, dreaming, and electrical stimulation of the brain, among other causes. It can also be deliberately induced by some. One in ten people has an OBE once, or more commonly, several times in their life.
Psychologists and neuroscientists regard OBEs as dissociative experiences occurring along different psychological and neurological factors.
Sleep paralysis
Those experiencing OBEs sometimes report (among other types of immediate and spontaneous experience) a preceding and initiating lucid-dream state. In many cases, people who claim to have had an OBE report being on the verge of sleep, or being already asleep shortly before the experience. A large percentage of these cases refer to situations where the sleep was not particularly deep (due to illness, noises in other rooms, emotional stress, exhaustion from overworking, frequent re-awakening, etc.). In most of these cases subjects perceive themselves as being awake; about half of them note a feeling of sleep paralysis.
Near-death experience
Another form of spontaneous OBE is the near-death experience (NDE). Some subjects report having had an OBE at times of severe physical trauma such as near-drownings or major surgery. Near-death experiences may include subjective impressions of being outside the physical body, sometimes visions of deceased relatives and religious figures, and transcendence of ego and spatiotemporal boundaries.