Yoga is very much a science of applied psychology, and a great deal of work has been done to distinguish and identify the various elements of the being in the development of the yogic science. The physical body is a framework that is inert without the action of the life energy, and thus, when the life energy, known as Prana, is withdrawn from the body, we say that the body dies. The prana provides all energy, both to the body and to the mental faculties, while taking various forms based on the action to be undertaken. The science therefore distinguishes between “physical prana” which operates the physical framework of the body, and “psychic prana” which enlivens the action of the mental being.
Sri Aurobindo emphasizes the importance of understanding the role of the Prana, because the loosening of the attachment to the body, and the rejection of its domination over the mental Purusha requires the seeker, at the same time, to reject and eliminate the impulsions of the pranic energy, which manifests as the various forms of desire, including physical drives such as hunger and thirst, and the vigor of the natural man in the forms of general health and outward drives of action, and the opposites in the form of fatigue and ill-health. The Taittiriya Upanishad has a lengthy exposition on the various sheaths that make up the life of man, starting with the gross outer physical body, the “food sheath”, and then the vital sheath constituted of the action of the prana, as well as further sheaths that become ever more subtle.
“Practically, in drawing back from the body we draw back from the physical life-energy also, even while we distinguish the two and feel the latter nearer to us than the mere physical instrument. The entire conquest of the body comes in fact by the conquest of the physical life-energy.”
“Along with the attachment to the body and its works the attachment to life in the body is overcome. For when we feel the physical being to be not ourselves, but only a dress or an instrument, the repulsion to the death of the body which is so strong and vehement an instinct of the vital man must necessarily weaken and can be thrown away. Thrown away it must be and entirely. The fear of death and the aversion to bodily cessation are the stigma left by his animal origin on the human being. That brand must be utterly effaced.”
At certain stages of the yogic development the seeker is directly confronted with the detachment of the consciousness from the life and body and the fear of death arises strongly at that moment. The first impulse is to shrink back from the experience that has brought this specific reaction, and if that impulse is followed, the seeker returns to the physical life of the body and does not pierce the barrier into a new realm of consciousness at that time. Eventually, this fear must be faced and overcome for the progress to continue and the evolutionary development beyond the bodily life to manifest.
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 7, The Release From Subjection to the Body, pp. 333-334