Yoga Nidra is an ancient form of motionless yoga that is essentially a guided meditation. Yoga is sanskrit for Union, and Nidra is sankrit for Sleep, so Yoga Nidra literally translates to the union of sleep. Yoga nidra brings people to a state between waking and sleeping, and most people fall into a deep sleep after it if they are not disturbed. The goal is to lay completely still. Experts believe that an hour of yoga nidra sleep is like a full sleep cycle. I find it an incredibly effective way to fall asleep at night, and it works for me about 9/10 times.

It's really important to have a great teacher. So many yogis teach Yoga Nidra but they don't understand the flow, or how it was practiced in ancient times, or when to pause, and for how long. So going to someone who hasn't really studied the practice at great length can be a poor experience that maybe prevents one from going to a good teacher in future. (Even my favorite free recordings have things I would change if they were mine.)