Yoga Nidra means "Yogic Sleep". This type of meditation brings us to a relaxed state, then takes us on a focused-attention tour of our bodies, slowly bringing us through the different brain wave states we encounter when falling asleep. This type of meditation activates the body's relaxation response, improving the function of our nervous and endocrine systems.
We start by moving from Beta (high brain activity state) to the more relaxed Alpha state through breathing and body scan, allowing for calm, a release of serotonin, and a balancing of the nervous system. We arrive at Theta state, where our REM sleep occurs (the same state we are led to during hypnosis), however, we are still awake. This state is where heightened learning happens.
Visualization exercises and affirmations are given while in Theta state before we are slow brought back out of the meditation.
It is said that 45 minutes of Yoga Nidra is the equivalent of 3 hours of deep sleep. This shows by an increase in energy after the meditation, if it's not done directly before bed.