In Meditation, you remain in the Waking state of consciousness, and gradually allow the layers of the unconscious and subconscious to come forward, expanding the Waking state with one-pointed concentration and non-attachment to the streams of impressions flowing in the field of mind.
In Yoga Nidra, you leave the Waking state of consciousness, and go to the Deep Sleep state of consciousness, yet, paradoxically, remain fully awake. It is an extremely relaxing state in which samskaras of attachment and aversion, the driving force behind karma, are attenuated in strength.
Reverie that is experienced between the Waking and Dreaming states, such as when you sometimes wake up in the morning with a pleasant half-here and half-there feeling, is not Yoga Nidra. This reverie is often the goal of relaxation and visualization exercises, but Yoga Nidra is far deeper.
Yoga Nidra brings access to the to latent, or subconscious level of mind, that is underneath even the processing, fantasizing, imaging level of mind. It is the doorway to the causal level of reality, out of which springs the subtle, psychic, astral plane of reality, which in turn brings forth the gross level.
Meditation and Yoga Nidra work together, as companion practices, through which you purify the deepest levels of the mind, and expand the conscious state to include what was previously unconscious. Finally, the expansion includes the realization of the pure consciousness that permeates all of the levels.
Seven Levels: The OM Mantra is a roadmap for sadhana, spiritual practices (written as either AUM or OM). It is not for the person who seeks only the shallow waters of spiritual life, but rather for those who strive to realize in direct experience the depth of the Absolute Reality. There are four main levels of consciousness outlined in the OM Mantra, along with three transition levels, which is a total of seven levels. Each of these is experienced on the inner journey of meditation and contemplation.
Universal Realities: It is important to be aware of the fact that these levels of consciousness are realities that exist universally, regardless of whether or not one uses the OM Mantra or the visual OM symbol in any way. In either case, the underlying principles are extremely useful for all seekers in purifying or clearing the mind, and seeking the direct experience of deeper truths.
Symbolism of the Oms in the Meditation hall at Abhyasa Ashram:
- Oms on the printed cloth on the wall: Vaishvanara, the gross realm of the waking state and the conscious mind.
- Shadow of the brass Om: Taijasa, the subtle realm of the dreaming state and the active unconscious mind.
- Brass Om: Prajna, the causal plane, the deep dreamless sleep state and the latent unconscious, the domain of samskaras that are the driving force of karma or actions.
- Lingam: Shiva lingam is the primary ground for manifestation. It is hiranyagarbha, literally the golden womb. On the inner journey it is experienced as the bindu that is pierced, transitioning to the realization of the Absolute Reality, Brahman, Shiva that is one and the same with Shakti (which is symbolized by the light, below).
- Light: Turiya, the fourth state of pure consciousness, Atman, Shakti, which projects outward through the deep impressions of the causal (the brass Om), manifesting in/as the subtle (the shadow) and, in turn, in/as the gross (the Oms on the wall cloth).
Yogic Conscious Deep Sleep by Swami Jnaneshvara Bharati at http://www.swamij.com/yoga-nidra.htm