Kundalini

The Kundalini is said to be the fundamental energy of the universe, coiled in the base of the spine of every (human) being. Awakened through the correct exercises (typically yoga and meditation, it can ascend through each chakra carrying the awareness of the practitioner with it, producing incredibly vivid experiences of many unusual kinds.

However, an attempt to rouse the kundalini which goes wrong can produce all kinds of varied and awful effects, including (according to sources like Gopi Krishna) mental and physical illness.

Promethea by Alan Moore has a particularly nice set of illustrations of a kundalini experience induced by sex magic.