Yoga nidra is a systematic method of inducing complete physical, mental and emotional relaxation. It is often referred to as psychic sleep or deep relaxation with inner awareness. In this threshold state between sleep and wakefulness, the subconscious and unconscious mind can be accessed and hence underlying impressions that are not helpful or bad habits or influences etc can be removed. This technique can also be used to develop memory, increase knowledge or creativity, or transform one's nature by planting a deep resolve when the mind is most receptive. For that to happen, you must deepen your relaxation by practicing regularly and allowing faith and positivity to sustain.

The technique described here has been taken from Bihar school of Yoga.

About the practice: Since you are required to lie down flat on your back with little to no physical movements throughout the practice, you might want to use a few props to get as comfortable as possible. The idea is to get the body to relax deeply so that the mind doesn't get distracted by any physical discomfort. If you are using a pillow under your head, make sure it's not too big or thick and that your shoulders are also rested on it. If it's hard for your knees to relax, try to put a small bolster under the knees. If your lower back is too arched, place a folded small blanket or a small towel under it. Experiment with a few adjustments that suit you. Above all, relax and let go.