probably a result of the natural DMT that;s released in the brain during near death experiences.
here's a link i just quickly looked up.
DMT (Dimethyltryptamine) is a naturally occurring psychedelic compound of the tryptamine family. DMT is Present Everywhere such as Plants and in Mammals. In Human it issecreted by Pineal gland. DMT plays a main role in Near Death Experience.
DMT is produced by our Pineal gland when we are asleep. It is usually secreted in smallquantities during REM sleep. But prior to death, it is secreted in large quantities which causeshallucinations that many peoples have experienced. These Hallucinations mostly occur in near deathexperience where the Patient was pronounced Clinically Death. During that Time the DMT is produced by the Pineal Gland in large quantities. The Hallucination produced by DMT are Reported by ManyPeoples. Some of the Feeling/experiences are
- Feeling of Exiting the Physical Body
- People Reported Clear Vision than Normal
- Going through a dark tunnel
- Encountering with light beings
- Sensation of being weightless and flying
- Having a life-review
- Meeting the deceased relatives/friends
to read more :
http://www.academia.edu/1970764/Role...ath_Experience 
