Sage Patanjali warns against sleep as a hindrance to yoga.+

The yogi, who follows Patanjali-yoga, wants to sit in a place and think "I’ am shutting my eyes, ‘I’ am sitting in this cave, and ‘I’ am meditating." This egocentric yoga has nothing to do with the ultimate truth or Brahman

The yogi mystic is always thinking in terms of me and ‘I’ for he thinks of what he is to get from his practice; whereas in the path of wisdom one first verifies and get rid of this ‘I’ by a deeper inquiry for he wants the truth, not something for the ‘Self’.

The Yogi says he wants to gain Samadhi. The Gnani wants to gain nothing for he knows, 'I’ is the whole universe."

Yoga is meant for the mass mindset, which is incapable of investigating and verifying their inherited beliefs.  The Atmic path is for realizing the pure essence of nonduality or Advaita.

Avadhuta Gita: ~ “The Atman cannot be purified through the practice of the six limbs of the yoga, or through the annihilation of the mind, or through the instruction of a teacher. The Atman is the Reality itself’ and It is Purity itself. "

From the standpoint of the Soul, the ‘Self’, the visions, and Samadhi are of the illusion because they are based on the false ‘Self’ (ego) within the false experience (waking).

It is not possible to stop the thoughts for more than a half-second whilst in the waking state. If one succeeds in controlling thought and then banishes it, one passes into Nirvikalpa Samadhi, which is identical to deep sleep. The only difference between ordinary deep sleep and Samadhi, therefore, is that the ordinary man falls asleep involuntarily whereas the yogi has the satisfaction of knowing that he has passed into sleep by his own effort of will in banishing thoughts.

Sage Patanjali warns against sleep as a hindrance to yoga, he means when it occurs in the early stages of the practice before one has obtained the power of control and consequently to banish the thoughts. The fact, that Samadhi is deep sleep is kept secret because people would not be tempted to take up yoga.

Yoga sharpens the ego, to enable it to keep away all extraneous thoughts when one gets out to reason in the practice of the next higher stage, i.e. Gnana.

Yoga is thus simply a sharpening stone for the ego to enable it to take up Gnana. But you say that Maharishi lives without thoughts, Impossible. How can he walk from one spot to another without thought? He does not know the Gnanic truth if he says thoughtlessness is the perfect stage of ‘Self’.

In Sutra Bashya and Mundaka: ~ Samadhi and sleep are identical. Brihad Upanishad does not advocate Samadhi. 

Bhagavan Buddha gave up his austerities of yoga as impossible and useless. (Page.70/71 "Buddhism in Translation” by Warren)

Bhagavan Buddha got enlightenment only after he gave up Yoga. Unless one exercises his reason--there is no chance of getting the truth.

When the yogi enters this highest Nirvikalpa (effort-less) Samadhi, he will at once enter deep sleep. This will make plain to him after he wakes, that the inner self he sought and found, the Atman, is reached only when all his ideas are refunded into it, when there is then all the features of non-duality, one without a second. However,  the yogi must later wake up, emerge from Samadhi and there is duality again, for the world of objects confronts him. So now he has to work on the next stage which is to find consciously in the waking experience the same non-duality that he unconsciously knew in sleep. This is done by learning that the universe is or idea or an object for the formless subject, and then refunding the universe,  ~idea back into its source, which is the Soul, which is present in the form of the consciousness. Only at this final stage,  he says "Atman, which is present in the form of the consciousness is the same as the Brahman. Brahman is the ultimate truth.  " Now he is fully aware of it.

All yogic visions, however, wonderful will pass away; they go as they come. They have the value of dreams. They are not the truth which is un-passing and beyond changes.

One can’t shut his eye to the universe, which confronts him as in Samadhi of yoga and see supreme reality. One can know it only by keeping himself clear and open.  Sage Sankara says:~   The yogi must add discrimination to his quest.

Nirvikalpa Samadhi and deep sleep are the same from the point of view of nonduality in the absence of the known. The knower was there. How does Samadhi give Gnana? Only by preparing the mind to see that the world disappears and re-appears and, that non-duality is here and duality there, to convince the man that in non-duality one won't disappear as he does not disappear in Samadhi or deep sleep. Another advantage of Samadhi is one gets the capacity to forget the external world and to treat it as an idea.

Yoga can never give you the fundamental thing, that the world is an illusion. Only Gnana can give it. Nirvikalpa Samadhi is unquestionably the same as deep sleep, and all ideas are refunded back there too. One must learn what ideas are when all the ideas of the universe's existence go back into one’s mind through Yoga. Then one learns this. How has he to learn that the entire universe is consciousness or Brahman if he stops at Nirvikalpa Samadhi? Without perceiving the universe, and having a duality before him, it is impossible.

Nirvikalpa has no duality, hence it cannot tell you about the universe. The yogi who emerges from Samadhi and says he found Gnana there, says it to a second person, hence there is duality again. If he were a real Gnani, there would be nobody for him to tell that he had experienced Gnana.

Self-knowledge will interest only a few people,  the rest are interested in Religion, yoga other paths, and pleasure hunting.:~Santthosh Kumaar