Yoga Nidra is a state of mind between sleeping and waking, such as the "sleep-to-wake" stage, usually induced by a meditative technique.
This technique involves visualization, relaxation, and deep breathing. The process of meditation in this state will induce deep states of awareness. For some people, this stage can even result in a trance-like state.
The state between awakening and falling asleep has been called a "trance," and for some, it may be called Yoga Nidra. It is generally experienced during REM (Rapid Eye Movement) sleep. When this state occurs, many dreams are possible. However, these dreams generally do not come true. Many people believe that this is a result of the brain being "unsettled." People with sleep disorders experience such a state because their brains are unbalanced. While this state is generally safe, it can cause serious health problems such as hypertension, seizures, or depression.
A common mistake in meditation is to allow thoughts to enter your mind while you are meditating. This leads to the mind of becoming highly active. Your mind is in a state of "paradigm" which allows it to accept new ideas. For example, when you are lying on your back with your hands clasped behind your head and your eyes closed, your mind is in a state of paradigm. During this state, your mind and body are very relaxed and open to suggestions. This state also enables deep relaxation in the muscles of the body.