In the second, third and fourth Raja-Yoga (Astanga-Yoga) sutras of Patanjali says:
Yoga is a restrain (control, termination) of vritti (fluctuations of consciousness), pertaining to the mind.
When vrittis are restrained, the meditator stays in his own nature.
Otherwise he has the shape of vritti (fluctuations of consciousness).
Therefore, training in Yoga is a means for controlling feelings and stopping of the mind, resulting in complete perception and the gaining of complete control of all of the material nature of one’s own being, as well as in understanding particular aspects of one’s own being.
The principal, in perceiving ones own nature in the practice of Yoga, is the «personal turn off mode», which is usually actuated by practicing Mrita Mudra in any «perfect sitting posture» («meditating») or in Savasana.
Mrita means «dead», mudra is a «state». Sarva means «corpse», whereas Asana, as you know, means «posture».
All exercises comprising Yoga complexes, i. e., Asanas, Vinyasas and Pranayamas, are varieties of actions: preparatory, auxiliary, or compensating, with respect to Mrita Mudra, which in any event implies concentration. But the Mrita Mudra itself is the absolute absence of actions and the termination of concentration. In order to enter correctly into it, one only needs to fully stop all activity and concentration.
Usually, people start to learn Mrita Mudra with various auto-training relaxation exercises, which, if perfected, are substituted with a quick deep relaxation of the whole body. Detecting the flows of imbalance in the “signal body” follows this. These will also balance and quiet down by themselves, like waves on the water. After that, only the «breath-mind» remains, and deep detachment from such «breath-mind» and the loss of interest in its «toys» leads one to stop thinking and to the voluntary attenuation of breath.
This state also has some background qualities, but they finally dissolve too. Contemplation itself loses any quality and the Contemplator dies away in Shanti (Peace), Movna (Silence) and Nirvikalpa Samadhi (no-quality balance of consciousness)…
Absent of energy consumers, i. e. the body, feelings and mind, require no energy for their activity. This state does not require even the slightest breath, and so breath is delayed naturally. The only thing that remains is Sat Chit Ananda — direct contemplation and pure perception in absolute non-action and bliss.
The process of such step-by-step detachment results in the perception of the «internal» human nature, appearance of the ability to disable particular organs and systems of the organism, so the practitioner becomes independent and free from any «external» impacts. This is how Moksa, Spiritual Liberation, is achieved.
Diving into Mrita Mudra results in becoming experienced in terminating suffering, which removes the fear of Death.
All acts of humans are, virtually, done without will, and their life energy and the Power of Spirit are irrevocably wasted. This volition is manifested through non-action with the absence of desires and striving for the objects of feelings, rather than through persistent actions. Only this process actually involves the Will and increases the Power of Spirit.
In conditions of modern life, diving into Mrita Mudra is, as a rule, time-restrained and not deep. However, even if this is the case, the dive still results in transformations of the consciousness, which make a man partially inadequate from the social point of view. In this state, a man may make some mistake or perform an inattentive deed, which may cost him his life or somebody else’s. Therefore, an obligatory element of the practice of Yoga in society is the «adaptation to social norms». A conscious «protective filter» is put into place, preserving «extra-marginal zones» of perception, or restricting perception to the generally accepted «norm». This is achieved by special actions, which are contrary to the «personal turn off mode» which must be practiced after Mrita Mudra.