Gnanic Samadhi is Sahaja Samadhi that is natural state of the self.

Sage Sri, Sankara says:- Yoga is not the means of liberation [page 132-133 of his commentary on Brihadaranyakopanishad]

Neither Yogic Samadhi or bliss or worldly pleasure should be allowed to draw one away from evenness; none of these  can give ultimate truth or Brahman. When the one is distracted by either, either internal or external bliss, it should by effort be drawn back to steadiness, evenness. This state alone yields the ultimate truth or Brahman.  Intellectually knowing the truth is only an imagination, whereas realizing the truth knows it as such.

Yogis assume that, thoughtlessness will give experience of ultimate reality. How can one keep out a portion of consciousness? It is utterly impossible. It is erroneous to say that such thoughtlessness experience is possible Moreover even if it were possible, what is it that the yogi will keep out? They will only be keeping out reality! The universe is none other than consciousness, as everything is consciousness. The yogi has got the idea of duality and therefore cannot realize truth.

Even the mind, which is in the form of universe disappear in deep sleep. Mind is changing and unreal. It passes away every moment. The consciousness appears as waking or dream [mind] and disappears as deep sleep (no mind).  

Yogic experience of bliss is not wisdom, for Bliss is something one have to experience, therefore it will have to go as it came; hence it is only part of the duality. Duality is an object to the formless subject. Yogis seek bliss through ignorance because he has accepted the ‘I’ as self.

The yogi who wants to go to mountains or an ashram to acquire self –knowledge has not risen above thinking of his body, and will not be able to acquire self-knowledge. For he wants to take his body from one place to another in the belief this will bring realization of the self.

Yogis make the fundamental mistake of assuming that these are things meditation or actions which are other than consciousness. The very idea they concentrate on is itself consciousness and hence needs no special effort. It is impossible to treat the mind as different from soul, which is in the form of consciousness. The Awareness i.e. consciousness must be there prior to all attempts to control the mind: therefore it is a fallacy to believe that any yogic exercise can create this awareness, this knowledge of self.

Katha Upanishad (Chap.4 V.12):- says:-  "Atman is meditated upon as the size of thumb in heart" i.e. for yogis who cannot concentrate without concrete picture, such an idea is useful. 

  Some sages declared Atman was in the heart, later with Patanjali in the lotus in the head.

If in the head it showed ignorance of relation between mind and brain.   When self, which is consciousness is immeasurable than how one can localize mind.  The consciousness is not limited to head or heart because it pervades the whole universe.  All these statements must not be believed but verified because deeper self-search revels the fact that, the self is formless, therefore question heart, brain, mind does not arise.

When Yogi comes out of Nirvikalpa Samadhi than immediately duality confronts him again. His peace goes, for it depended on the non-duality of Samadhi-sleep. Hence no yogi attains true peace, but imagines it.

When one sees second thing and though seeing it know it to be consciousness, then he get Gnana. On the other hand, Nirvikalpa Samadhi is the non-seeing of the second thing; hence cannot yield Gnana, for the yogi does not see and does not know what the universe is.

If one grasps and understands and assimilates non-duality then it is impossible to have any doubt. And doubt is the essence of error, mistake and delusion. Those who are not established in non-duality have to guess, or imagine, i.e. doubt.

Yogi says everything is Brahman, but cannot prove it. The Gnani says the same thing; even this universe is Brahman, but he can prove it.

If one feels ecstatic or exalted peace in the presence of yogi or mystic is not the truth it is mere feeling. People, who are disturbed, agitated, troubled, unhappy finds tranquility at Ashrams, because there was restlessness, probably over business, family or finance etc. But that is because they do not know truth and they mistake this peace for Brahman or ultimate truth. It merely indicates the state of mind possessed on arrival at Ashram; they had a mental disease and the ashram cured it for the time. There is no permanent cure however without Gnana, and Yoga does not yield Gnana.

If one is imaginative or poetic, mysticism and religion is suitable for him, but not path of wisdom.   In religion there is element of imagination. Ordinary peoples have limited view and they like their religion because it gives them some sort of   satisfaction and please their taste.  Wisdom discards religion and yoga because they are based on the false self and false experience.

Emancipation can occur without yoga. What can be done by yoga can be done by Gnana. Yoga alone leads to Samadhi, but Gnana also liberates one from experiencing the illusory experience of birth, life, death and the world as reality. .

If it is said that one gets Gnana in yogic Samadhi in which there is no duality, it is no better than deep sleep. If it be said that there is a direct cognition in profound contemplation in which there is no difference between the perceiver and the perceived and in which no duality can occur; then why not admit the same in deep slumber.  If it be objected that there is no knowledge of the nature of self [soul or Atman] in deep sleep, then one admit that self-  knowledge only is true knowledge and not the absence of duality.

That consciousness remains as the sole real factor, means that there should be self – realization that is, Consciousness as the sole entity and not a not a mere absence of the cognition of the universe; otherwise there would be no such thing as emancipation in this life.

Those people, who talk of experiencing the supreme reality, do not know that the word experience implies something else, a second to be experienced, i.e. duality, i.e. non-reality, and those who talk of "direct knowledge" of reality again do not perceive that knowledge implies a second thing to be known; i.e. duality exists. i.e. no reality here!

To know the supreme reality means to know the complete negating of all that is not this reality. Hence one does not make an object of it.

The notion of attaining Nirvikalpa Samadhi, complete blankness, non-seeing the universe is for those who are still in fancy stages in their pursuit of truth. The universe must be seen but known for what it is, mental.

Many yogis teach that Brahman is in the top chakra of the skull; that therefore we have to ascend there. This is mere imaginary theory based on the false self or ego. Nirvikalpa Samadhi helps one to renounce attachments, it is a corrective medicine to remove this disease; hence it is for seekers only who are still on the disciplinary or infancy level. For peace of mind does not necessarily indicate truth; one can get it by taking opium or ganja.

Yogic Samadhi cannot get one Gnana. Yoga is useful in preparatory stages. Realization thro’ yoga is merely bait to seekers to adopt his preliminary state, but it is not literally true. Yoga cannot give Gnana. Those with weak minds tire soon and cannot keep up the concentrated inquiry into truth, the three states etc. without which one cannot grasp nonduality and their real meaning.

Some texts in some of the Upanishads which assert that the soul returns to Brahman in Samadhi are another form, a different standpoint. When one sees all the three states, that is one standpoint, but when he is in waking experience and takes his stand on that, the view is lower and different. If opponent says world is real from waking experience, then a different argument is given him from one who can understand Mandukya and see it as idea. Mandukya Upanishads alone gives the ultimate truth basis. The other Upanishads treat from a lower standpoint to help beginners.

One who is in Samadhi will not know that this universe is consciousness; therefore yoga is not the means to self- knowledge. In Samadhi the yogi knows nothing, sees no universe; so if there be nothing whatever, how can yogi know that the universe which is something is consciousness? If the universe is not seen in Samadhi than why are word Atman and Brahman are used?

By shutting his eyes in Samadhi yogi do not know the universe, which confronts him. Hence the universe can't be known as Brahman through yoga alone. One is in a non-dual condition in sleep or Samadhi, One without a second, true, but he did not know it at the time. You say only in the waking experience afterwards. Hence there must be inquiry so that you find non-duality whilst you are awake, so that you can see non-duality at the time not afterwards. Hence too the need of inquiring into the universe and knowing it as Brahman whilst one is awake, and not during sleep or Samadhi.

When can one say there is no error in his knowledge? When one sees all the three states as consciousness, which the true self; then there will be no doubt. Hence one must see the beings and objects, if he is to see them as consciousness, the true self. But sleep and Samadhi does not show them to him. Hence their knowledge is not perfect, not free from error and doubt.

The completion of the course of Yoga, whether Raja or Dhyana leads as Patanjali rightly says in sloka 1 to stopping of all ideation. When this is attained, only one thing can then occur--the yogi will enter a condition like sleep. "Like," because he will have done it by set effort and voluntarily, whereas ordinary man falls into sleep involuntarily and when Patanjali lists sleep as one of the five hindrances, he means that while a practitioner is still struggling and has not yet attained his goal of concentration, naturally to fall asleep prematurely is a sign of failure.

The ignorant emerging from deep sleep does not regard his body and his experience of the world as consciousness, which is the true self but he thinks he is an individual separate from the world. Hence he feels duality as reality, similarly, with the yogi. The one, who does not see duality, can have no Gnana. A Gnani sees, and says all this is illusion made out of consciousness, which is the true self. Hence there is unity in diversity, whereas, the yogi who enters Samadhi or sleep has none to start with.

Gnanic Samadhi is Sahaja Samadhi that is natural state of the self. In natural states in which self is in full wakefulness, and then one asks what is meant by this universe, the universe is seen in this Sahaja Samadhi. Whereas Yogic or Nirvikalpa Samadhi, is just like swoon or deep sleep, where one is unaware of anything, not even the universe. [See page 640,641 and verse 132,133 of Tattireya upanishad and panchadeshi regarding this].