It is said that the history of yoga nidra is as old as yoga itself, as the first mention of yoga nidra is in the Upanishads. Lord Krishna is associated with yoga nidra in the epic Mahabharata.
At well-equipped laboratories Swami Rama demonstrated conscious entry into NREM delta wave sleep through yoga nidra, whereas his disciple was able to demonstrate delta and theta waves even with eyes open and talking
Reference Rama, Swami (1982). Mandukya Upanishad: Enlightenment Without God. ISBN 978-0-89389-084-1.
Yoga nidra meditation is associated with increased endogenous dopamine release in the ventral striatum of the brain. The reduced desire for action in the state is associated with the reduced flow of blood in parts of the brain connected with controlling actions, the prefrontal cortex, the cerebellum and the subcortex.
Yoga nidra improves heart rate variability, a measure of balance in the autonomic nervous system, whether or not it is preceded by a session of hatha yoga asanas.
The regular practice of yoga relaxation has been found to reduce tension and anxiety. The autonomic symptoms of high anxiety such as headache, giddiness, chest pain, palpitations, sweating and abdominal pain respond well. It has been used to help soldiers from war cope with posttraumatic stress disorder (PTSD). A 2019 study suggests that yoga nidra can alleviate stress and improve self-esteem of university students
Simply said the practice is to see all 5 elements within the body Air Water Fire Earth and Ether. And to keep the mind in a relaxed state keeping away and removing the 3 strains