Sympathetic and Parasympathetic Balance in Yoga Modern physiology explains balance in terms of the sympathetic and parasympathetic branches of the autonomic nervous system . Health depends not on suppressing either branch, but on their rhythmic alternation across the day. Traditional yogic physiology describes this same alternation using the language of sun (surya) and moon (chandra) . These are not metaphors layered onto physiology; they are functional categories derived