An out-of-body experience essentially refers to the phenomenon when the consciousness of a person is detached or separated from the physical body, making it exist or travel outside of it. However, the person can understand what is happening around him or hear the conversations taking place around him. This experience is also called astral projection or astral travel

George N. M. Tyrrell had first introduced this term in 1943 in his book "Apparitions", which was soon embraced by researchers like Robert Monroe and Celia Green as a substitute to labels centered on beliefs, like spirit walking, soul travel or astral projection. This phenomenon was described by Waldo Vieira, another researcher, as a prognosis of consciousness.

There are a number of things that can induce out of the body experiences or OBEs. These include brain traumas, sleep, near-death experiences, dehydration, psychedelic and dissociative drugs, sensory deprivation and electrical stimulation of the brain.

According to mainstream science, an OBE is a kind of hallucination which can be a result of one or several neurological or psychological factors. It is also considered by certain occult writers and parapsychologists as proof of the fact that a spirit, soul or subtle body is capable of detaching itself completely from the physical body and traveling to distant locations.

Robert Monroe categorized out of the body experiences into two types, namely Locale 1 and 2.

In case of Locale 1, there is considerable consistency between reality and the environment. The person experiencing it may perceive extreme physiological sensations such as racing heartbeat, full body vibrations and electrical tingling, all of which could be really frightening. It is very natural to suffer from confusion in this type of experiences. This is because the person can have the feeling that he has died or awakened physically and his limbs seem to penetrate other objects, which can lead to panic.

In contrast, Locale 2 experiences are not so much openly physical in nature. The overlap is much more subjective and dreaming more lucid. An immersion in unrealistic worlds or altered forms of reality happens for the person involved. He also exhibits inconsistent or physically impossible features.

The first person to do a scientific study on the phenomenon of OBEs was Celia Green. First-hand, written accounts from as many as 400 subjects were collected by her for the purpose of providing a categorization of the varied forms of OBE.

Again, the subject was approached by Dr. Robert Crookall from a spiritualistic perspective. It was reported by most of his subjects that the physical body was connected with its observing counterpart with a cord. This was in stark contrast to Green's findings in which 80% of her subjects reported that they felt like a disembodied consciousness without any external body.

Are OBEs harmful?  According to the Bible and some other religious texts, any kind of occult practices should be avoided as they are a kind of sorcery or divination, however if they occur spontaneously how could they be considered as "practices"?

Irrespective of whether they are harmful or not, OBEs continue to be experienced and experimented by people all over the world.