DMT, The Spirit Molecule, by Rick Strassman, M.D. Are really good read, even for atheists.
Here is his website.
Here are the basics.
Dr. Strassman actually got the go-ahead from the government, including the DEA, to research DMT, the most powerful psychedelic substance known. The DMT molecule is present in most all other psychedelic substances as well as some neurotransmitters, including:
ibogaine (anti-addiction hallucinogen)
psilocybin (magic mushrooms)
DMT is ubiquitous in plants and animals throughout the world. It is theorized that DMT is released by our pineal gland and is responsible for dreams, NDE's (Near Death Experiences), OBE's (Out of Body Experiences), spiritual experiences, and, bet this, alien abduction experiences.
The reports from volunteers in his study reported all of the above after DMT injections in a controlled clinical setting.
Listen to actor/comedian Joe Rogan talk about DMT.