The Origin and Clinical Relevance of Yoga Nidra.

Yoga nidra, also known as 'yogic sleep', is a simplified form of an ancient tantric relaxation technique. The most general description of the practice is that it combines guided mental imagery with a specific yoga posture called Shavasana (or "corpse pose"). The goal of yoga nidra is to promote a profound state of relaxation, which differs from sleep inasmuch as there is still an awareness of one's surroundings. While several components of the practice have been known since ancient times, it was not until the 1960s that an updated and systematized system of practice was introduced to the public through the writings of Swami Satyananda Saraswati. Unlike other schools of yoga, which emphasize concentration or contemplation, yoga nidra's goal is complete relaxation. As such, its advocates claim that it is suitable for all individuals, from beginners to advanced practitioners of yoga. The calm inner stillness induced by yoga nidra is claimed by practitioners to be an effective stress management tool as well as a means for attaining greater receptivity to personal resolutions. These resolutions can range from the goal of achieving self-transformation, enhancing creativity, or improving one's learning ability. Additionally, yoga nidra is claimed to promote beneficial changes in physiological and mental health. The following narrative review summarizes the basic steps used to achieve the final state of yoga nidra relaxation as well as some recent experimental findings regarding its physiological and psychological effects. Standard research databases were searched for relevant articles. Clinical studies have shown that yoga nidra meditation is associated with positive physiological changes, including improvements in several hematological variables, red blood cell counts, blood glucose levels, and hormonal status. Two neuroimaging studies have shown that yoga nidra produces changes in endogenous dopamine release and cerebral blood flow, a further confirmation that its effects on the CNS are objectively measurable. The practice has also been shown to reduce psychometrically measured indices of mild depression and anxiety, although these benefits were not shown in an experimental study to extend to severe depression or severe anxiety.