Restorative yoga is a practice in which the psyche, nervous, and immune systems have a chance to rest. When the body is in a state of stress, adrenal glands release hormones that act on the autonomic nervous system (again, fight or flight response) which in turn increase the heart rate, blood pressure, muscle tension. When the adrenals are over-worked, other systems, like digestion, elimination, growth, repair, and reproduction shut down. This is often the result of a build-up of stress which can initiate of cycle of stress-related diseases such as: high blood pressure, ulcers, back pain, immune dysfunction, reproductive 
problems, colitis, insomnia, indeigestion, constipation, depression, and of course, anxiety (which all of these disorders often re-create!). People with high-blood pressure, exhaustion, chronic fatigue, or general agitation have neurons that are worn out due to excessive activity. Restorative poses provide an environment for the neurons to recover - giving rest to the brain so that certain chemicals (like serotonin) are secreted. This active relaxation undoes our modern problem of chronic stress--offering the body an opportunity to heal itself.
Asanas which move the spine in a variety of directions (including forwardbends, twists, and supported backbends) enhance the exchange of oxygen and waste products across the cell membrane. They help sooth nerves and relax the brain, relieving stress-related headaches, migraines, chronic fatigue syndrome, hypertension, palpitations and breathlessness (among other respiratory, glandular, spinal problems).
Both soothing and regenerating, these poses bring balance to our demanding daily lives, allowing us to release tension at deep levels and experience an increased sense of well-being.These are meditative poses in which the body is at rest because it is supported. Props allow the posture (whether a forwardbend, backbend, twist, or inversion) to be held without strain for extended periods of time. Recent neurological research shows that 20 minutes in a well-supported restorative pose is equivalent to 2 hours of deep sleep in terms of bone, muscle, and cell regeneration and brain-wave activity.