Kundalini (kuṇḍalinī, Sanskrit: कुण्डलिनी) literally means coiled. In yoga, a “corporeal energy” – an unconscious, instinctive or libidinal force or Shakti, lies coiled at the base of the spine. It is envisioned either as a goddess or else as a sleeping serpent, hence a number of English renderings of the term such as ‘serpent power’. The kundalini resides in the sacrum bone in three and a half coils and has been described as a residual power of pure desire.
Kundalini is described as a sleeping, dormant potential force in the human organism. It is one of the components of an esoteric description of man’s ‘subtle body’, which consists of nadis (energy channels), chakras (psychic centres), prana (subtle energy), and bindu (drops of essence).
Kundalini is described[who?] as being coiled up at the base of the spine, usually within muladhara chakra. The image given[who?] is that of a serpent coiled 3 and a half times around a smokey grey lingam. Each coil is said[who?] to represent one of the 3 gunas, with the half coil signifying transcendence.
Through meditation, and various esoteric practices, such as kundalini yoga, laya-yoga, and kriya yoga, the kundalini is awakened, and can rise up through the central nadi, called sushumna, that rises up inside or alongside the spine. The progress of kundalini through the different chakras leads to different levels of awakening and mystical experience, until the kundalini finally reaches the top of the head, Sahasrara chakra, producing an extremely profound mystical experience.
A number of descriptions exist that attempt to describe exactly what the kundalini experience is.
Sri Ramana Maharshi maintained that the kundalini energy is nothing but the natural energy of the Self, where Self is the universal consciousness (Paramatma) present in every being, and that the individual mind of thoughts cloaks this natural energy from unadulterated expression. Advaita teaches that Self-realization, enlightenment, God-consciousness, nirvana and kundalini awakening are all the same thing, and self-inquiry meditation is considered a very natural and simple means of reaching this goal.Yogis, there are two nerve currents in the spinal column, called Pingalâ and Idâ, and a hollow canal called Sushumnâ running through the spinal cord. At the lower end of the hollow canal is what the Yogis call the “Lotus of the Kundalini”. They describe it as triangular in form in which, in the symbolical language of the Yogis, there is a power called the Kundalini, coiled up. When that Kundalini awakes, it tries to force a passage through this hollow canal, and as it rises step by step, as it were, layer after layer of the mind becomes open and all the different visions and wonderful powers come to the Yogi. When it reaches the brain, the Yogi is perfectly detached from the body and mind; the soul finds itself free. We know that the spinal cord is composed in a peculiar manner. If we take the figure eight horizontally (∞) there are two parts which are connected in the middle. Suppose you add eight after eight, piled one on top of the other, that will represent the spinal cord. The left is the Ida, the right Pingala, and that hollow canal which runs through the centre of the spinal cord is the Sushumna. Where the spinal cord ends in some of the lumbar vertebrae, a fine fibre issues downwards, and the canal runs up even within that fibre, only much finer. The canal is closed at the lower end, which is situated near what is called the sacral plexus, which, according to modern physiology, is triangular in form. The different plexuses that have their centres in the spinal canal can very well stand for the different “lotuses” of the Yogi.
According to well-known teacher and translator Eknath Easwaran, kundalini means “the coiled power,” a force which ordinarily rests at the base of the spine, described as being coiled there like a serpent.
The kundalini rises from muladhara chakra up a subtle channel at the base of the spine (called Sushumna), and from there to top of the head merging with the sahasrara, or crown chakra. When kundalini Shakti is conceived as a goddess, then, when it rises to the head, it unites itself with the Supreme Being (Lord Shiva). Then the aspirant becomes engrossed in deep meditation and infinite bliss.
The arousing of kundalini is said by some to be the one and only way of attaining Divine Wisdom. Self-Realization is said to be equivalent to Divine Wisdom or Gnosis or what amounts to the same thing: self-knowledge. The awakening of the kundalini shows itself as “awakening of inner knowledge” and brings with itself “pure joy, pure knowledge and pure love.”
The question arises: how is this awakening triggered? There are two broad approaches to kundalini awakening: active and passive. The active approach involves systematic physical exercises and techniques of concentration, visualization, pranayama and meditation under the guidance of a competent teacher. These techniques come from any of the four main branches of yoga but for this purpose could be termed kundalini yoga. The passive approach is instead a path of surrender where one lets go of all the impediments to the awakening rather than trying to actively awaken the kundalini. A chief part of the passive approach is shaktipat where one person’s kundalini is awakened by another who already has the experience. Shaktipat only raises the kundalini temporarily but gives the student an experience to use as a basis.
The spiritual teacher Meher Baba emphasized the need for a master when actively trying to awaken the kundalini: “Kundalini is a latent power in the higher body. When awakened it pierces through six chakras or functional centres and activates them. Without a master, awakening of the kundalini cannot take any one very far on the Path; and such indiscriminate or premature awakening is fraught with dangers of self-deception as well as misuse of powers. The kundalini enables man consciously to cross the lower planes and it ultimately merges into the universal cosmic power of which it is a part, and which also is at times described as kundalini….The important point is that the awakened kundalini is helpful only up to a certain degree, after which it cannot ensure further progress. It cannot dispense with the need for the grace of a Perfect Master.”
The experience of kundalini awakening can happen when one is either prepared or unprepared.
According to Hindu tradition, in order to be able to integrate this spiritual energy, a period of careful purification and strengthening of the body and nervous system is usually required beforehand. Yoga and Tantra propose that kundalini energy can be “awakened” by a guru (teacher), but body and spirit must be prepared by yogic austerities such as pranayama, or breath control, physical exercises, visualization, and chanting. Patanjali emphasised a firm ethical and moral foundation to ensure the aspirant is comfortable with a reasonable degree of discipline and has a serious intention to awaken their full potential. The student is advised to follow the path in an openhearted manner.
The kundalini can also awaken spontaneously, for no obvious reason or triggered by intense personal experiences such as accidents, near death experiences, childbirth, emotional trauma, extreme mental stress, and so on. Some sources attribute spontaneous awakenings to the “grace of God”, or possibly to spiritual practice in past lives.
A spontaneous awakening in one who is unprepared or without the assistance of a good teacher can result in an experience which has been termed as “kundalini crisis”, “spiritual emergency” or “kundalini syndrome“. The symptoms are said to resemble those of kundalini awakening but are experienced as unpleasant, overwhelming or out of control. Unpleasant side effects are said to occur when the practitioner has not approached kundalini with due respect and in a narrow egotistical manner. Kundalini has been described as a highly creative intelligence which dwarfs our own. Kundalini awakening therefore requires surrender; it is not an energy which can be manipulated by the ego.
Physical effects are believed to be a sign of kundalini awakening by some, but described as unwanted side effects pointing to a problem rather than progress by others. The following are either common signs of an awakened kundalini or symptoms of a problem associated with an awakening kundalini:
- Involuntary jerks, tremors, shaking, itching, tingling, and crawling sensations, especially in the arms and legs
- Energy rushes or feelings of electricity circulating the body
- Intense heat (sweating) or cold, especially as energy is experienced passing through the chakras
- Spontaneous pranayama, asanas, mudras and bandhas
- Visions or sounds at times associated with a particular chakra
- Diminished sexual desire or a state of constant orgasm
- Emotional purgings in which particular emotions become dominant for short periods of time.
- Pressure inside the skull and headache
- Bliss, feelings of infinite love and universal connectedness, transcendent awareness
A personal experience was described by Brian Van de Horst: he felt an activity at the base of his spine starting to flow so he relaxed and allowed it to happen. A feeling of surging energy began traveling up his back, at each chakra he felt an orgasmic electric feeling like every nerve trunk on his spine beginning to fire. D. R. Butler describes a similar experience accompanied by a wave of euphoria and happiness softly permeating his being. He described the surging energy as being like electricity but hot, traveling from the base of his spine to the top of his head. He also reported that the more he analyzed the experience, the less it occurred.
Reports about the Sahaja Yoga technique of kundalini awakening suggest the practice can result in a cool breeze felt on the fingertips as well as on the fontanel bone area. One study has measured a drop in temperature on the palms of the hands resulting from this technique.
Comparisons with other religious systems
The tantras of Vajrayana manage a system which is very similar to the Indian systems of kundalini yoga, in that they too manage a series of subtle channels, subtle winds, wheels and subtle drops, and they refer to a force known as kandali which must be raised up the central channel. However, there are a number of differences. Firstly, the descriptions are mostly about ‘red bodhicitta‘, that resides in the lower chakras, and ‘white bodhicitta‘, that resides in the crown. The ‘inner fire’ is ignited, through practices such as Tummo, which causes all the winds in the body to enter and rise up the central channel. When the fire reaches the crown of the head, the white bodhicitta melts and flows down to the lower chakras, producing profound spiritual experiences of bliss and emptiness.
This practice of ‘inner fire’ is seen as a preliminary yoga to a further set of practices; obtaining the ‘Illusory body’, and obtaining the ‘Clear Light’, as well as practices such as dream yoga, and consciousness projection.
Kundalini is considered an interaction of the subtle body along with chakra energy centers and nadis channels. Each chakra is said to contain special characteristics  and with proper training, moving kundalini energy ‘through’ these chakras can help express or open these characteristics.
Sir John Woodroffe (pen name Arthur Avalon) was one of the first to bring the notion of kundalini to the West. As High Court Judge in Calcutta, he became interested in Shaktism and Hindu Tantra. His translation of and commentary on two key texts was published as The Serpent Power. Woodroffe rendered kundalini as “Serpent Power” for lack of a better term in the English language but “kundala” in Sanskrit means “coiled”.
Western awareness of the idea of kundalini was strengthened by the Theosophical Society and the interest of the psychoanalyst Carl Jung (1875–1961). “Jung’s seminar on kundalini yoga, presented to the Psychological Club in Zurich in 1932, has been widely regarded as a milestone in the psychological understanding of Eastern thought. Kundalini yoga presented Jung with a model for the development of higher consciousness, and he interpreted its symbols in terms of the process of individuation”.
Sri Aurobindo was the other great authority scholar on Kundalini parallel to Sir John Woodroffe, with a somewhat different viewpoint, according to Mary Scott (who is herself a later day scholar on Kundalini and its physical basis) and was a member of the Theosophical Society.
Another populariser of the concept of kundalini among Western readers was Gopi Krishna. His autobiography is entitled Kundalini: The Evolutionary Energy in Man. According to one writer his writings influenced Western interest in kundalini yoga.
In the early 1930s two Italian scholars, Tommaso Palamidessi and Julius Evola, published several books with the intent of re-interpreting alchemy with reference to yoga. Those works had an impact on modern interpretations of Alchemy as a mystical science. In those works, kundalini is called an Igneous Power or Serpentine Fire.
Other well-known spiritual teachers who have made use of the idea of kundalini include Swami Rudrananda (Rudi), Yogi Bhajan, Osho, George Gurdjieff, Paramahansa Yogananda, Swami Sivananda Radha who produced an English language guide of Kundalini Yoga methods, Swami Muktananda, Bhagawan Nityananda, Nirmala Srivastava (Shri Mataji Nirmala Devi),and Samael Aun Weor.
Kundalini references may commonly be found in a wide variety of derivative “New Age” presentations, such as Shirley MacLaine‘s, and is a catchword that has been adopted by many new religious movements. However, some commentators, such as transpersonal psychologist Stuart Sovatsky, disapprove of New Age authors and groups who have appropriated certain Yogic Sanskrit terms, such as chakra, kundalini, and mantra, and defined them in ways that relate only superficially, if at all, to the traditional meaning of the words. 
Recently, there has been a growing interest within the medical community to study the physiological effects of meditation, and some of these studies have applied the discipline of Kundalini Yoga to their clinical settings. Some modern experimental research seeks to establish links between kundalini practice and the ideas of Wilhelm Reich and his followers.
The popularization of eastern spiritual practices has been associated with psychological problems in the west. Psychiatric literature notes that “since the influx of eastern spiritual practices and the rising popularity of meditation starting in the 1960s, many people have experienced a variety of psychological difficulties, either while engaged in intensive spiritual practice or spontaneously”. Among the psychological difficulties associated with intensive spiritual practice we find “kundalini awakening”, “a complex physio-psychospiritual transformative process described in the yogic tradition”. Researchers in the fields of Transpersonal psychology, and Near-death studies have described a complex pattern of sensory, motor, mental and affective symptoms associated with the concept of kundalini, sometimes called the Kundalini Syndrome.
According to the psychiatrist Carl Jung, “…the concept of Kundalini has for us only one use, that is, to describe our own experiences with the unconscious…”
resource : wikipedia