Let’s understand why the Yogic wisdom of “cooling down” is important from the lenses of modern Neuroscience.
In any stressful situation during your normal daily routine (including fear, worry, and anxiety) or even a planned activity that challenges the body (like Sports, Exercise or an active Yogasana practice), the Hypothalamus (the control center for the Autonomic Nervous System (ANS)) is aroused.
To prepare the body for the threatening or challenging situation, the Hypothalamus directs the Adrenal Medullae to release a mixture of stress hormones into the bloodstream. These stress hormones – Epinephrine and Norepinephrine (in 80:20 ratio) are collectively known as “Catecholamine”. If the situation is a perceived threat, another stress hormone called “Cortisol” is also released. The Hypothalamus activates almost all of the components of the Sympathetic Nervous System (SNS) to prepare the body for flight-and-flight response. This results in constriction of the blood vessels, dilation of bronchioles in the lungs, an increase in the heart rate, dilation of the pupils of the eyes, glycogenolysis of glycogen in the liver into glucose (for the brain and muscles) and so on. Consistent elevated levels of these stress hormones and Sympathetic Nervous System overdrive creates neurological and physiological disorders that are very common in the modern world like hypertension, depression, anxiety and even diabetes.
Hence, it is important that you alleviate or control stress-producing situations. Once the situation is cleared completely, it typically takes 20 minutes or so for the Catecholamine and Cortisol to be cleared from the bloodstream, and overactivation of the Sympathetic Nervous System to calm down. And then the body returns to the pre-arousal level.
This “relaxation response” is the reason why Yogasana sessions are recommended to conclude with a cooling down sequence ending with Savasana. This allows the body, breath, and mind to attain homeostatic hormonal and emotional balance – and produce a peaceful level of consciousness and a quieter mental state.
Many other therapeutic, relaxing and rejuvenating practices (like Transcendental Meditation, Warm-water immersion therapy) also rely on this 20-minute relaxation response.