Here is an excerpt from a scholarly work on Yoga that explores similarities between pranayama (yogic breathing technique) with Hesychasm:
An interesting problem is raised by Hesychasm. Some of the ascetic preliminaries and methods of prayer employed by Hesychastic monks offer points of resemblance with yogic techniques, especially with pranayama. Father Irenee Hausherr thus summarizes the essentials of Hesychastic prayer: "It comprises a twofold exercise, omphaloskepsis and indefinite repitition of the Prayer of Jesus: 'Lord Jesus Christ, Son of God, have mercy on me!' By sitting in darkness, bowing the head, fixing the eyes on the center of the abdomen (in other words, the navel), trying to discover the place of the heart, by repeating this exercise indefatigably and always accompanying it with the same invocation, in harmony with the rhythm of respiration, which is retarded as much as possible, one will, if one preseveres day and night in this mental prayer, end by finding what one sought, the place of the heart, and, with it and in it, all kinds of wonders and knowledge."
Here is a short passage, recently translated by Jean Gouillard, from Nicephorous the Solitary (second half of the thirteenth century): "As for you, as I have instructed you, sit down, compose your mind, introduce it-your mind, I say-into your nostrils; this is the road that the breath takes to reach the heart. Push it, force it to descend into your heart at the same time as the inhaled air. When it is there, you will see what joy will follow; you will have nothing to regret. As the man who returns home after an absence cannot contain his joy at again being with his wife and chidren, so the mind, when it is united with the soul, overflows with joy and ineffable delights. Therefore, my brother, accustom your mind not to hasten to depart from thence. At first, it has no zeal-that is the least that can be said-for this enclosure and confinement within. But once it has contracted the habit, it will find no more pleasure in wanderings without. For 'the kingdom of God is within us,' and to him who turns his gaze upon it and pursues it with pure prayer, all the outer world becomes vile and contemptible."
In the eighteenth century the doctrines and techniques of Hesychasm were still familiar to the monks of Athos. The following extracts are from the Encheiridion of Nicodemus the Hagiorite. "Beginners must accustom themselves to performing this return of the mind as the divine Fasting Fathers have taught, bowing the head and pressing the beard against the upper part of the chest." "Why the breath must be held during prayer. Since your mind or the act of your mind is from childhood accustomed to disperse and scatter itself among the sensible things of the outer world, therefore, when you say this prayer, breathe not constantly, after the habit of nature, but hold your breath a little until the inner word has once spoken the prayer, then breathe, as the divine Fathers have taught. Because through this momentary holding of breath the hard and tough heart becomes thin, and the humidity of the heart, being properly compressed and warmed, becomes tender, sensitive, humble, and more disposed to compunction and to shedding tears freely...Because during this short holding of the breath the heart feels uneasiness and pain, and through this uneasiness and this pain, it vomits the poisoned hook of pleasure and sin that it had swallowed."
Finally, we must cite the fundamental treatise, the Method of Holy Prayer and Attention, long attributed to Simeon the new Theologian..."Then seat yourself in a quiet cell, apart in a corner, and apply yourself to doing as I shall say: close the door, raise your mind above any vain or transitory object. Then, pressing your beard against your chest, direct the eye of the body and with it all your mind upon the center of your belly-that is, upon your navel-compress the inspiration of air passing through the nose that you do not breath easily, and mentally examine the interior of your entrails in search of the place of the heart, where all the powers of the soul delight to linger. In the beginning, you will find darkness and stubborn opacity, but if you persevere, if you practice this exercise day and night, you will find-O wonder!-a boundless felicity." Finally, other Hesychastic texts could be cited-for example, Gregory of Sinai(1255-1346), some important passages from whose writings are given in Gouillard's 'Petite Philocalie'. The apology for Hesychasm by Gregory Palamas (c. 1255-1346), "the last great name in Byzantine theology," can be consulted with interest.
But we must not be deceived by these external analogies with pranayama. Among the Hesychasts respiratory discipline and bodily posture are used to prepare mental prayer; in the Yoga-sutras these exercises pursue unification of consciousness and preparation for meditation, and the role of God (Isvara) is comparatively small. But it is none the less true that the two techniques are phenomenologically similar enough to raise the question of a possible influence of Indian mystical physiology on Hesychasm. We shall not enter upon this comparative study here.
From "Yoga: Immortality and Freedom" by Mircea Eliade, pp.63-65.
While some of the techniques in Yoga have similarity with Hesychast techniques, especially when a person is in the preparatory stage of either tradition, they radically depart when a person moves beyond these introductory stages. In Yoga, the purpose of mental and bodily exercises are to free the mind from its attachments to worldly forms, which are themselves an illusion created by us because of a false ego. In earlest known Yoga philosophy, there is a concept of one God (Isvara), however there is not a distinction between Isvara and our being in essence. The difference between Isvara and humans is our state, in that Isvara was never enslaved by illusion and therefore is not subject to pain like we are. Yet we or God are neither creator or created, just derivation of a primordial unity. Out of sympathy, Isvara will help a Yoga practitioner who has set upon the Yoga path to freedom from illusion, but this is something that happens automatically because a person is able to break free of illusion, and therefore becomes recognizable as a free spirit by Isvara (and in theory returns to Isvara accordingly as the only distinction from Isvara is illusionary). Of course, this teaching is largely ignored in most modern Yoga studios, which simply focus on the basic initial asana(posture)/pranayama(breathing/attentino) techniques, which is only a part of the whole Yoga methodology and philosophy.
In comparison, these ideas are far from the Orthodox understanding that there is no similarity between us, or any creation, and God in Essence. God is the Father and Creator, we are His creation. Techniques in the path of Orthodox christian prayer are not geared towards breaking an illusionary world, but rather breaking our wrong orientation and psychic attachments to a very real world that has been subjected to our sinfulness. In every case, we call upon God for aid in recognition that even though we must make effort, which involves our will, we cannot break free of our worldly attachments without grace or help from God. Hence orthodox spiritual practice has a subject: our Lord and God Isa the Christ.
I have some speculations about our Orthodox spiritual practice. I personally see hesychasm is a practice that is rooted in the earliest stages of mankind's self-conscious existence on this planet and was born at a time when people still had experiential memory of communion with God (which I can't describe because that time is long gone). It does not surprise me that in the current form, it comes from the same region of the world that the earliest 'civilization' comes from - Kemet and other regions historically associated with Kemet through the greater mediterranean region, asia/india and east Africa. In light of that, what we call Hesychasm is simply the organic, traditional practice of calling on the name of the Lord, in each point of time expressed in recognition of the progressive revelation of God through His creation. Our history, tradition reflects this continuity from our earliest scriptures.
Similarity in Hesychast and Yogic techniques, techniques that were passed down through generations, may suggest a common root rather than an influence of Yoga on Hesychasm. Where the Yoga tradition represents a natural philosophy apart from the corrective energy of revelation, Hesychasm is the product of natural, historical human self-knowledge under the influence of divine revelation. Our orthodox Liturgical counterpart, also under the influence of divine revelation in the context of organic human transmission, include postures that have meaning and purifying effect combined with praise and supplication. This is a methodology that simultaneously includes all aspects of our nature - physical, mental, emotional - and goes hand-in-hand with "hesychast" spiritual practice and is related to it.
Again, the strong, essential role of Grace, of the energies of God, always present in Tradition since Cain and Abel, could explain why the techniques of our christian practice have not been overemphasized and subsequently developed to the degree Yoga has. Seeing that there is an underlying belief that freedom from "fallen state" rests entirely on the Yogin, there is no boundary between the source of life and illusionary life such as the boundary of Creator and creation. So if God is not creator, and no different than us (just not in our painful illusionary state), overcoming pain becomes the measure of spiritual progress, motivating the Yogic tradition to be as advanced as it is from a natural point of view. In the Christian tradition, we certainly treat wounds and heal pain, but this is not the ultimate end of what we are doing here. Our enemy is death, and it is very real. For me, Yoga is very useful in dealing with physical pain and anxiety, and I have found that my experience practicing the techniques of asana and pranayama have even helped me to understand a small amount of what Ive received from our orthodox fathers (purely from the point of view of calming the mind in preparation of attending prayer). But these things are not really spiritual per se, they are at best pre-spiritual. Nevertheless, its always nice to not be overwhelmed by stress, weighed down by "the world". However, there are points of departure in Yoga that I recognize and see no use in putting any of my energy into mainly because they are unprofitable imaginings as far as Im concerned. Christ says "my yoke is easy, my burden is light" which I believe describes an asceticism that can only result from grace. in this biblical case "yoke" is thought to be derived from the same sanskrit word: yoga.
"God is the Lord and has revealed Himself to Us, Blessed is He that cometh in the name of the Lord."