Kundaini yoga is a term referring to a set of ritual practices mainly in Tantric Hinduism, involving a set of physically based meditation exercises designed to utilize the human body as a means of spiritual enlightenment. Kundalini yoga is a form of laya yoga as described in the Yogatattva Upanishad.
In the Kundalini Concept: Its Origin and Value, “Tantric science and therefore also its yoga was, and still is, a body-affirming system. Unlike yoga advocating its denial and seeing bliss and enlightenment as involving the transcendence of physical limitations, the Tantric yogi seeks to raise up the quality of natural forces so that enlightened states can be [experienced] within the body”. The culmination of this practice is the ability to move the Kundalini energy (a form of shakti) “coiled” at the base of the spine upwards through the seven, or twelve major chakras and eventually up and out of the body through the “crown” at the top of the head.
This process is an extreme physical and energetic act which, if not properly guided, can produce disastrous physical and mental results, sometimes causing a state resembling psychosis. But according to the Tantric texts, with proper preparation and the support of a guru, the flow of Kundalini force through the chakras can lead to supreme bliss and mystical revelatory experience.
Philosophically, Kundalini occupies the somewhat curious metaphysical position of being a non-physical force which is located or mapped onto the physical body. In this sense, the system of Kundalini and the chakras is a scientific -- but bodily subjective -- process of exploring how energy interacts with matter. This practice is associated mythologically and cosmologically with the figures of the god Siva and goddess Shakti as the two necessary and balancing vital spiritual forces which combine to create material reality. Thus the Tantric worldview could be described in the context of Western philosophy as an Idealist view, wherein the immaterial energies of Shakti and the underlying structure of Siva, although themselves non-material, as thought to construct and give birth to the material world. According to some interpretations, Taoist alchemical practices were functioning according to similar philosophical assumptions. In Serpent of Fire: A Modern View of Kundalini, Darrel Irving describes how “etheric” or “subtle” energy may be thought to interact with the human body in the philosophy of Kundalini.
The kundalini process occurs in what is sometimes called the etheric or subtle (nonphysical) body, this etheric body may actually be physical, composed of atoms and cells just like all other parts of the body. This subtle body is comprised of nerve fibers not visible to the naked eye. For the sake of visualizing this system, therefore, imagine these fibers as looking like all the nerves and ganglia of the nervous system, some as thin and spindly, others as thick and clustery, all of them radiating light, and branching out through the entire body, thousands of them. Their overall appearance in the body might be likened to the grid of electric lights one sees above a city at night. These nerve fibers are actually conduits. They are called Nadis; some are major, some are minor, and their function is to conduct currents of energy called prana, or vital force, throughout the body. Not only does this prana animate the body, but it is this force that can be controlled by the Yoga adept through various exercises, described below, to activate the kundalini.
The kinds of exercises involve cultivating breath control techniques, trance states, body postures, visualizations, and other elements of yoga. However, there are documented cases of people outside of the tradition of yoga or Hinduism experiencing something which can be interpreted as a Kundalini awakening .
Another aspect of the Kundalini energy that is important to understand is the fundamentally sexual nature of the Kundalini. The Kundalini energy is conceived as a generative force which carries some of the same connotations of the Freudian psychological concept of libido energy. When interpreting ancient religious ideas it may be difficult to discern between the elements of a texts that may be describing something literally, or metaphorically, or both. Certainly, though, the Kundalini energy has been interpreted as being closely associated with the material sexual fluids, most obviously male sperm. Thus non-ejaculation and redirection of sexual energy internally (also referred to as “reversal of sexual energy”) is one of the most crucial teachings of Kundalini sexual practices. The full development of Kundalini through the chakras is only possible if the sexual energy that arises is contained within, and not spilled in the form of external ejaculation. Spilling the sexual fluid is thought to result in a hastening of death and degeneration of the vitality of the subject.