Contrary to what most people are saying, the theory that it is released during death/NDEs/OBEs, etc is just a THEORY because present day ethics will not allow a living human brain to be opened and looked at for the presence of DMT.
DMT is the slang term for "Dimethyltryptamine" or "N,N-Dimethyltryptamine."
However, it is an intense psychedelic tryptamine endogenous to many animals/plants including humans. Average dosage is between 15-60mg and can be smoked/injected or if taken with an MAOI ingested orally. The experience can be described as loading the universe into a cannon and firing it at your brain. It's effects are short lived, lasting around 10 min, and completely done within the hour.