Imagery of snakes and serpents often appear in sacred poetry and art. This can cause confusion because Christian iconography focuses so heavily on the image of the serpent in the Garden of Eden as an expression of evil or the Devil. But among Eastern spiritual traditions (as well as pre-Christian traditions in Europe), snakes represent the Divine Feminine. And in Yogic terminology the snake is the sacred Kundalini Shakti, the energy of spiritual power found within each individual as well as the power of manifestation in the universe.
In most individuals this energy is coiled up and dormant at the base of the spine. Through spiritual practice and stillness of mind, or occasionally through trauma, the Kundalini is awakened and it rises up the spine to the crown.
Sometimes this rising of the Kundalini serpent can be so powerful that trembling or, in extreme cases, convulsions and unconsciousness result. Spiritual practice and increasing familiarity with the energy minimizes these more disruptive expressions.
Although initially overwhelming, the awakening of the Kundalini is a profoundly blissful, liberating state of awareness that beautifully clears the mind. Reality is perceived directly, without the coloring of our "normal" mental filters. Everything is new and alive in a way not perceived before.
When you allow yourself to go deeply into the awakening of the Kundalini, your normal sense of identity, the little self, the ego, disappears. There is no "you" left, just the radiant state of Being.
The shift in consciousness is so profound that it is often compared with waking up after a deep sleep. It is the initiation of spiritual enlightenment.
Snakes and the Kundalini also represent specifically women's power. Although the shape of a snake is phallic, its serpentine movement and ability to shed its skin bring to mind the cycle of seasons and the moon -- feminine expressions in nature.
The Kundalini itself is considered a Goddess or an expression of the Goddess energy within Hindu traditions. It is the feminine aspect of the (apparently) divided spiritual energy. When it is awakened and rises, it rejoins the masculine aspect of the Divine (Shiva) which resides at the crown (the mountaintop).