Do some research on DMT. The "near death" experience is more likely than not due to when you clinically die your pineal gland in your brain releases a ton of DMT and you have one of these experiences. DMT has a hallucinogenic effect like LSD, however with DMT the hallucinations have similar elements.
The pineal gland, sometimes referred to as the third eye can be connected to many "mystical" experiences, visions, and so on. The mind is a powerful thing. Do a little research into the experiments that were done in the 60's i believe, many people had similar experiences with beings etc that could be compared to both alien abductions and near death (biological not clinical) experiences.