Yoga Nidra Pro app for iPhone and iPad

Yoga nidra or "yogic sleep" is a state of consciousness etween waking and sleeping, like the "going-to-sleep" stage. It is a state in which the body is completely relaxed, and the practitioner becomes systematically and increasingly aware of the inner world by following a set of (audio) instructions. This state of consciousness (yoga nidra) is different to meditation in which concentration on a single focus is required. In yoga nidra the practitioner remains in a state of light pratyahara  with four of his senses internalised (withdrawn) and only the hearing still connects to the instructions. The yogic goal of both paths, deep relaxation (yoga nidra) and meditation are the same, a state called samadhi.
Yoga nidra, lucid sleep, is among the deepest possible states of relaxation while still maintaining full consciousness. In lucid dreaming, one is only (or mainly) cognizant of the dream environment, and has little or no awareness of ones actual environment.
The practice of yoga relaxation has been found to reduce tension and anxiety. The autonomic symptoms of high anxiety such as headache, giddiness, chest pain, palpitations, sweating and abdominal pain respond well.