Yoga is essentially a spiritual discipline based on extremely subtle science, which focuses on bringing harmony between mind-body and thought-action with ultimate goal to attain self-realization of one’s soul with the cosmic consciousness. It is an art and science of healthy holistic lifestyle which is open for all to access, implement & propagate with its higher purpose to create well-being amongst all the religions & communities in this one world. The word 'Yoga' is derived from the Sanskrit root 'Yuj', meaning 'to join' or 'to yoke’ or 'to unite’. As per Yogic scriptures the practice of Yoga leads to the union of individual consciousness with that of the Universal Consciousness, thus indicating a perfect harmony between the mind and body, Man & Nature. According to modern scientists, everything in the universe is just a manifestation of the same quantum firmament that weaves the cosmic fabric of particles & its observer (i.e. consciousness). One who experiences this subjective feeling of oneness of existence after practicing the principles of Yoga (i.e.Sadhana) is termed as a Yogi, having attained a state of freedom from attachments, referred to as nirvana. Living with freedom in all walks of life, health and harmony shall be the main objectives of Yogic practices. Hereby, we attempt to briefly review yoga and various yogic practices in context of implication as complementary treatment modality for modern diseases having their origin from stressful lifestyle of 21st century.
Yoga had been the ancient still prevailed lifestyle practice basically having its roots from Eastern wisdom. The term, 'Yoga' is derived from the root, 'yuj' which means to yoke together or unite. Yoga has been used for millennia as a tool for self-improvement, with the ultimate goal of uniting the individual consciousness with the universal. Sage Patanjali (100BC), who codified its practices into an eight-limbed model (Ashtanga Yoga) in the Patanjali Yoga Sutras, makes it clear that the target of yoga is primarily the mind  as the practice of yoga deepens our understanding of the links between body & soul, through the vehicle of mind. The Eight Limbs of Ashtanga, are: Yama- Moral codes, Niyama- Self-purification & study, Asana- Posture, Pranayama- Extension of Breath, Pratyahara- Withdrawing of the mind from the senses, Dharana- Mental fixation, Dhyana- Deep meditation and Samadhi- Union with the object of meditation . These Ashtanga signify the step by step journey from physical body to the discovery of mind & self-realization of the soul or spirit and the ultimate self-actualization with the cosmic consciousness. Yoga is the final annihilation (Nirodha) of all the mental states (Cittavrtti) through progressive stages to attain a steadied mind with particular types of graduated mental states. The ultimate goal as described by Patanjali is the attainment of a particular spiritual mind state through Selfrealization (understanding seer swarupa or true state of self), termed as drastu and to overcome all kinds of sufferings leading to the ultimate state of solitude or detachment (i.e. Kaivalya).
Across the ages since the last few centuries, different schools of Yogic practices have been observed to gain popularity in the society, based upon the prevailing socio-cultural factors but the core concepts were the same as mentioned in Ashtanga. Some schools gave more emphasis over the practice of Asanas that lead to the sudden burst of Hatha Yoga in the community & it attracted vast attention owing to complex visual impression of the stances attained during its practice (for example- Sheershasana & some other physical postures demonstrating extensive flexibility of physical bodies). These practices required great physical agility and although popular, Asanas were not feasible to practice for one and all, leading to its confinement limited within a population. Then gradually, some other schools started focusing over Pranayama (Praana + Aayaama) which focused over extending the breathing capacity through different techniques in order to fuel the praana to attain the ultimate goals of yogic practices. The techniques in Pranayama needed to be practiced in seated position without any discomfort to the body. The focus was on Unit of life (i.e. Breath) which had its direct implications over oxygenation of the brain thus, preparing it for achieving higher states of Asanas and Pranayama formed as helpful tool to teach the disciples of yoga about how & when to hold on and to let go; physically as well as mentally. Their action over calming the heightened sympathetic nervous system and thus regulating the hypothalamo-pituitary-adrenal (HPA) axis has documented evidence in reduction of stress levels which has found to be beneficial in reduction of morbidity of some physical and mental diseases having co-relation with cortisol levels . These scientifically quantified results cum benefits of practicing Pranayama are found to be analogous to the subjective pratyaksha pramana as experienced by the eminent disciples of yoga. The Pranayama slowly gained its space in the late 20th century when the population was overburdened with the lifestyle related stress and had started facing the physical consequences of it: in the form of cardiac illness including heart attacks & hypertension, various metabolic disorders such as diabetes, thyroid irregularities etc. The goal of the disciples was to cure their physical bodies and it had minimal focus over the diseased mind. It was nevertheless to mention that Pranayama has its role only as a complementary to the modern medicine and not alike the propaganda made initially as a curative measure. Then, another school of Yoga emerged to balance this duality of physical body & mind with the focus on Kundalini (literal meaning: serpant power) which hypothesized dormant energy chakras aligned along the spinal meridian that are activated upon the release of primal energy at Mulaadhar chakra which is situated at the root of spinal column. Kundalini Yoga had its primary focus over the breathing through separate nostrils on alternate mode (similar to Anulom-Vilom Pranayama) and the sensations felt thereafter in the head and spinal region which had some suggestibility component to the followers of this school of Yoga. This had created its base in many communities owing to its basics related with the easiest form of Pranayama and some preliminary non-randomized evidence as an alternative therapy for some forms of mental illness . Later on, many simplified methods of Dhyana (such as - Mindfulness & Transcendental Meditation) were demonstrated and popularized by various schools of Yoga that deployed methods of concentration or non- judgmental momentary awareness of various senses of body and undivided focus on Mantras or Sounds. Dhyana gained early popularity due to evidence based reduction of stress, primary prevention of cardio-vascular disease  and attainment on individual peace along with social harmony.
With the emergence of modern treatment modalities for metabolic diseases (such as cardiac illness, obesity etc) which once contributed as one of the most important contributor to global morbidity and mortality, it has been speculated by a report  by World Health Organization that the mental illness; specifically the depressive disorders & suicide are projected to override Disability Adjusted Life Years (DALYs) with that due to cardiac diseases in 2020. With this apprehension and the limitations in pharmacological interventions in the cure of psychiatric illness having its Bio-psycho-social etiology, there had been various attempts to study the role of various Yogic practices as alternative therapy in management of mental diseases like depression and schizophrenia. Benefits of yoga in treatment of psychiatric conditions have been corroborated by several positive physiological effects such as- Reduction in cortisol; increases in neurotropic factors (BDNF), plasma oxytocin; heart rate variability, amplitude of the cognitive event related potential, and increase in hippocampal gray matter volume, as reported in different studies [3,7,8]. Specific stances (i.e. Asanas) have been found to be useful in alleviation of negative symptoms and defunct facial expression recognition in mental illness like schizophrenia and depression . Generation of such positive evidence in the treatment modalities of mental disorders has lead to designation of Yoga as ‘Yoga Therapy when used scientifically, as evidence based adjunctive treatment modality. Yoga therapy though having tremendous potential forits utility in psychiatry should be rigorously checked to produce generalizable, level 1 empirical evidence . Yoga therapy can be deployed not only as preventive measure but also as rehabilitative & to rejuvenate during recovery phase after major physical and mental illness. Day by day, increasing evidence of Yoga therapy has been demonstrated not only at physiological level but also to be associated with epigenetic modification  with reduction in inflammatory mediators related to DNA methylation and possibly reduced Telomerase activity . Results have demonstrated overall well-being with better cognitive abilities and improved quality of life in geriatric population. It was not to the surprise that United Nations felt the necessity to spread Yoga as lifestyle modification, declaring 21st June as International Day of Yoga, with theme for 2017 Celebration-“Yoga for Health'.
We can see how the Yogic practices have been shifted rather bypassed purposefully over the hundreds of years from some basic limbs of Ashtanga (such as Yama, Niyama & Pratyahara) and then focused on the other higher limbs directly (viz., Asanas,Pranayama, Dhyana & Samadhi). With the rapid changes in lifestyle, the ethics & moral codes of society today have been altered gradually and may not be according to the standards set by Patanjali (100BC). Even for any kind of illness, doctors admit the patients in ICU and 'do not allow many visitors' and insist from refraining from one's routine work. This kind of practices have prevailed the Pratyahara alive in today's sensation pleasing consumer world where Pratyahara had became the most difficult limb of Ashtanga to practice independently. The practice of Dhyana as a rocket to directly attain Samadhi (which is the highest goal of Ashtanga Yoga) has ruined the foundation of Ashtanga laid by the visionary sage Patanjali. We can observe the subtle sequential goals to be attained during Ashtanga-Yogic practices where expertise in each step forms the foundation for the next higher goal to be attained- Yama & Niyama make the self-purification feasible at physical bodily level; Asanas make the physical body amenable to next step of abstinence from pleasures (i.e. Pratyahara); Pranayama nourishes the pranic mental energy to make the mind ready for Dhyana & Dharana and then, finally the Samadhi experience may be attained after total detachment & liberation from birth-death cycle. Nevertheless, this kind of fragmented simplification of Yoga has been ultimately implicated in wide publicity & acceptability of Yoga as lifestyle modification in different communities in the world. May be attaining mastery over all the Eight Limbs of Ashtanga remain as the highest goal (i.e. Samadhi) for dedicated disciples of Yoga, but for general population of 21st Century who aim at Yoga as a adjunctive therapy for betterment of their individual health, the liberty to make choice & follow lies over people themselves and of course, over the recommendations by trained therapist based upon the available scientific evidence in literature. The evolving scientific advances to quantify various agama pramanas (i.e. quantitatively demonstrated effects of Yoga over various systems in physical body and its co-relation with the mind) shall surely lure the upcoming generations in understanding the core principles of Ashtanga Yoga through practice itself and this shall safeguard the perpetual existence of this ancient wisdom which has already prevailed through ages apart. Considering the recent world-wide recognition, Time is no far when Yoga shall become the basic integral part of life of every individual and each community.