Shavasana is a posture in Yoga that resembles that of a dead body. In Shavasana, all the muscles of the body are in a relaxed condition. One of the important steps in savasana is performed by lying down in a supine position, like a corpse. Benefits of Shavasana include removal of fatigue and putting the mind to rest, as described in Hathayogapradipika (I.32).
Shavasana is usually practiced at the end of postural exercises and before the practice of pranayama. When the muscles are already exercised, they can be brought to a relaxed state more easily. Relaxation involves withdrawal of motor impulses flowing from the brain to the muscle fibers. Such withdrawal means silencing a portion of the brain. To achieve this important effect, a little practice under instruction from a teacher is required.
Lying down on the back on a carpet spread on the floor, keeping a comfortable distance (about a foot or more) between the heels, the whole body is placed comfortably without feeling any stress, pull, or discomfort at any part. Keeping the eyes closed, attention is paid to individual body parts from the toes upward, one by one, and the state of relaxation is felt progressively from the toes to the eyelashes. Another round of mental attention brings superficial relaxation.
Next comes deep relaxation. For that, it is necessary to stop two activities completely. One is silent talking to oneself, and the other is seeing images as words are uttered unknowingly. Most of the thoughts arising in the mind issue from these two activities. Hence they must be abandoned in order to put the mind to rest. This is perhaps the most difficult part of savasana. With practice, the flow of words and images can be stopped completely, and if the muscles are also relaxing then the state of deep relaxation can be achieved. That is the ideal state of Shavasana.