|The dreams of man|
|Disturbing your sleep|
Mysticism is a communion with the divine, either through esoteric knowledge or directly through revelation or meditation. Mystics come in all flavors, from the deeply sincere to the outright fraudulent.
While all mystics believe in something divine, not all believers are mystics. There are many branches of Christianity, for instance, which frown on this kind of direct communion, instead preferring rational argumentation and discovery of God through texts. However, Eastern Orthodox Christianity and, to a lesser degree, Roman Catholicism employ mysticism in theological discourse.
 Natural explanation
Mystical experiences are frequently induced by stressing the body through hunger, thirst, sleep deprivation, stressing the mind through isolation. All this can cause hallucinations as can drugs that are used to induce mystical experience. There is every reason to believe mysticism is due to natural processes in the brain.