Yoga nidra is a type of guided meditation that translates to "yogic sleep." During the practice of yoga nidra, one is in a state between dreaming sleep and wakefulness, so that there is more awareness compared to when a person is asleep. The practice consists of being guided by instructions through connecting to a sankulpa (or "resolve"), breathing, rotating awareness through the body, guided visualization, and exploration of opposite sensations and emotions. From this practice, one can fully relax the mental, emotional, and sensation systems. Yogis see yoga nidra as a beneficial practice for relaxing, training the mind, lowering muscle tension, increasing creativity, clearing out the unconscious, lowering stress, lowering symptoms of psychological disorders, and improving mental functions like memory and learning. The practice has been studied in recent years for its applications such as insomnia, depression, anxiety, and PTSD.
To practice yoga nidra, find place where you can either lie down on your back or sit in a supported chair, such as a recliner. Make sure that you feel comfortable before beginning the practice. You may want a blanket or cover as your temperature may drop during the practice. Listen to the instructions and follow them without moving or falling asleep. Discontinue any practice that does not feel comfortable for you.
There are many yoga nidra recordings available, and I have provided one below. The recording is about thirteen minutes long.