The elephant is a great example of this. A dying elephant will leave the herd so that it doesn't slow them down. However, this theory doesn't explain why near death experiences are so erratic.
The Hallucination Theory suggests that near death experiences are caused by a "dying body secreting endorphins which act on the central nervous system causing "runner's high", which happens when long distance runners go through a pain barrier and find themselves running with ease and without tiredness, and with a feeling of elation." (www.near-deathexperiences.com). However, endorphins are not hallucinogens. Their role is more of a painkiller. Still skeptics will say that seeing a bright light that emits love and peace or having loved ones meet you in the light to guide you on the rest of the journey is merely the .
essence of one's life, flashbacks if you will, to help the mind deal with the trauma of dying. If near death experiences are only hallucinations, why do so many people report being told, "It's not your time to die" or "You still have tasks to complete"? If this is just a hallucination, then how could so many people be hallucinating the same thing? Mass hallucination? I don't think so.
Lastly, is The After-Life Theory. Dr. Kenneth Ring, perhaps the most respected of all near death experience researchers, says, "Any adequate neurological explanation would have to be capable of showing how the entire complex of phenomena associated with the core experience would be expected to occur in subjectively authentic fashion as a consequence of specific neurological events triggered by the approach of death I am tempted to argue that the burden of proof has now shifted to those who wish to explain near-death experiences in this way."(www.near-deathexperiences.com). What he is saying is that near death experiences are similar in many aspects that it's going to be hard to find a physical explanation for them.