To quote Albus Dumbledore: "Of course it is happening inside your head, Harry, but why on earth should that mean that it is not real?"
I did a little research on this "Leu-enkephalin", and from what I can gather, it's an opioid peptide (a chemical which produces a reaction similar to that of opium) neurotransmitter, meaning it enables that specific chemical to travel efficiently throughout your system. Not sure how that correlates to your theory, but there you go.
Personally, I am a strong believer in free-will and consequence. I don't have any reason to believe that a deity is pulling the strings. However, I could see the sense in believing that an impartial entity runs the universe, sort of like a groundskeeper or janitor. I believe in spirit guides, although I am aware that mine exists inside my head (The Dumbledore quote is relevant here again). She just helps me project good, happy thoughts, which I really need.
