Yoga nidra is a meditative practice introduced by Swami Satyananda Saraswati that is not sleep or concentration. It helps open the inner chambers of the mind. The practice involves rotating awareness through different parts of the body, experiencing sensations like heaviness and lightness, visualizing objects, and awareness of the chakras to relax the body and mind. Yoga nidra has benefits for conditions like insomnia, drug addiction, pain, pregnancy issues, psychosomatic disorders, and cardiovascular diseases.