Interesting article...

...in the New Scientist "The Collection" publication on the human brain. Research shows that epileptic fits of the partial seizure type can lead to feelings of intense well-being, a feeling of oneness with the universe and even religious rapture.   Amongst others, Dostoevsky reported these kind of feelings.

Another article reports that your gut bacteria (which weigh about the same as your brain, and have many hundreds of genes) can affect your mood and well-being via the mind-altering chemicals they produce.