Etymology and origins
The earliest mention of this asana is in the 15th century Hatha Yoga Pradipika 1.32, which states that "lying full length on the back like a corpse is called Savasana. With this asana, tiredness caused by other asanas is eliminated; it also promotes calmness of the mind." 
Shavasana and other sitting asanas maintain the balance between relaxation and meditation (two key components of yoga) by their equal input of physical stimuli.
To perform Shavasana, lie on the back with the legs spread as wide as the yoga mat and arms relaxed to the side, preferably with no props. The eyes are closed and the breath is deep with the use deergha (long) pranayama. The whole body is relaxed on the floor with an awareness of the chest and abdomen rising and falling with each breath. During Shavasana, all parts of the body are scanned for muscular tension of any kind. Any muscular tension the body finds is consciously released as it is found. All control of the breath, the mind, and the body is then released for the duration of the asana. Shavasana is typically practiced for 5–10 minutes at the end of an asana practice, but can be practiced for 20–30 minutes.
The asana is released by slowly deepening the breath, flexing the fingers and toes, reaching the arms above the head, stretching the whole body, and exhaling while bringing the knees to the chest and rolling over to the side in a fetal position, drawing the head in the right arm. From here, one can push themselves up into a seated position.
Savasana is intended to rejuvenate the body, mind, and spirit. In Savasana, practitioners’ breath deepens, and the stress of the day is released. The yogi forgets all other thoughts and surrenders any psychological effort. While in Savasana, yogis slip into blissful neutrality and reflect on the practice.
Comfort is essential in the asana; the slightest point of discomfort can be endlessly distracting. Shavasana is a good way to reduce stress and tension. On the other hand, yoga-nidra ("yogic sleep") meditation is often practiced in a lying position. Drowsiness or restlessness of the mind while in Shavasana may be counteracted by increasing the rate and depth of breathing. While in Shavasana, it is important to be in a neutral position. Practitioners who find it hard to relax in Shavasana may do better by bending the knees and moving the feet hip-distance apart.
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