Most of the beneficial effects of yoga nidra cannot be measured with scientific instruments. This is especially true of the profound changes that occur in the mind. However, various scientific tests have detected and measured the following physiological changes which occur in the body during yoga nidra.
Respiration. There is a dramatic reduction in the oxygen requirements of the body. This is a consequence of the reduced metabolic rate of the body The respiration rate also reduces – there is slow, deep breathing instead of fast, shallow breathing.
Heart rate. There is a profound reduction in the heartbeat. The blood pressure, both systolic and diastolic, is drastically reduced.
Brain wave pattern. There is a measurable decrease in the brain wave frequency, the change being mainly from beta to alpha activity. The alpha waves are known to be associated with relaxation, peace and a feeling of well-being. Occasionally, the lower frequency theta waves have also appeared in people doing yoga nidra. These indicate even deeper relaxation and possibly meditation.
Sympathetic nervous system. There is a detectable dampening down of the sympathetic activities of the body. These are generally associated with stress, fear and overactivity of the mind and body.
Blood lactate. The lactate level in the blood has been scientifically correlated with stress. During yoga nidra there is a striking and easily measurable reduction in the lactate level in the body.
There are various other measurable physiological changes in the body, such as skin resistance. These changes can occur during deep sleep, but it takes some hours. Yoga nidra induces a deeper state of relaxation, allowing these beneficial changes to take place in a shorter period of time.
In the future there should be systematic research into the effects of yoga nidra. An important field of research and investigation should be the effect of yoga nidra on the endocrinal glands. Another thing that needs to be done is to photograph a person with Kirlian photographic techniques, firstly before practising yoga nidra, then during yoga nidra and after completing yoga nidra. This will give clear indication of the changes that occur in the pranic body, including expansion of the aura. Many people know that this occurs from their own experience and perception, but scientific proof would be invaluable.