BYoga Nidra basically is a way of reaching a state of deep meditation, lying down in Savasana position
and therefore avoiding the typical discomforts of seated meditation. 

The Sanskrit term “Yoga Nidra” translates into “yogic sleep”, a technique of deep relaxation and a form of meditation. Also called “psychic sleep”, Yoga Nidra represents a state between sleep and wakefulness, where the body is completely relaxed and the practitioner turns the consciousness inward by listening to a series of instructions – much like a guided meditation. Performing yoga nidra involves practicing pratyahara (“extraction of the senses”), which is the fifth branch of Ashtanga Yoga. 

Yoga Nidra is derived from the ancient tantric Nyasa practice. It is an important technique of meditation and deep relaxation developed by Swami Satyananda Saraswati who adapted and updated the ancient practices, preserving their essence, while removing their ritualistic complexity, adapting them to our time and making them more accessible to anyone. 
 
The practice of Yoga Nidra produces deep relaxation and expands the individual’s self-awareness,
among other important mental and physical benefits: 
– Calms the mind 
– Relaxes and rejuvenates the body 
– Relaxes the nervous system 
– Reduces fatigue 
– Reduces high cholesterol and blood pressure levels  
– Strengthens the immune system 
– Improves sleep quality 
– Helps with depression 
– Reduces pain 
– Improves concentration 
– Supports brain function and increases creativity 

One hour of Yoga Nidra is equivalent to 4 hours of deep sleep. I discovered this by “causality” on my first Vipassana Meditation retreat and it changed forever the relationship I had had with insomnia throughout my life.