From Out of your head: Leaving the body behind:
During sleep paralysis, it is possible to enter a REM-like state in which you dream of moving or flying. Under these circumstances you are conscious of a sensation of movement, yet your brain is aware that your body cannot move. In an attempt to resolve this sensory conflict, the brain cuts the sense of self loose (Cortex, vol 45, p 201). “It resolves by splitting the self from its body,” says Cheyne. “The self seems to go with the movement and the body gets left behind.” Perhaps similar sensory conflicts cause classic out-of-body experiences….
[T]he study of out-of-body experiences promises to help answer a profound question in neuroscience and philosophy: how does self-consciousness emerge? It’s abundantly clear to us that we have a sense of self that resides, most of the time, in our bodies. Yet it is also clear from out-of-body experiences that the sense of self can seemingly detach from your physical body. So how are the self and the body related?
From what i have read the OBE can occur strongly by offsetting the sleep schedule so that you wake up before REM sleep progresses, then nap later in the day, wake up, go to bed again at the normal time. The brain is trying to make up for lack of REM by kind of forcing it on you.
Another method is called WILD (wake induced lucid dream) where you wake up earlier than usual then try to go back to sleep to induce a lucid dream by remaining aware as the body sleeps.
Why the brain would produce an OBE i have no idea, but i am not totally convinced that dualism doesn’t exist. It is quite likely possible that once a human is concieved in the womb a type of double energy body blueprint comes into existence together with the physical body and at death the physical body is cast off. After all, science is now saying that more than 90% of the universe is unknown. It’s not too much of a stretch to postulate the existence of subtle matter smaller than electrons etc.
It’s tempting to go for material explanations in the absence of personal experience of something spiritually significant. But people who have superconscious experiences have a different view.