The the following talks, Bhagavan Sri Ramana Maharshi outlines a very simple but powerful teaching, that of wakeful-sleep or Jagrat-Sushupti (Jagrat means the waking state, Sushupti means deep dreamless sleep). This teaching in essence is no different to the other teachings of Sri Ramana Maharshi, and is also no different to the great Vedanta teachings, but is just another way of expressing the same principle.
The method consists of noting that in deep dreamless sleep the mind is still and there is no suffering, but there is also no awareness of this fact at the time. In the waking state we are presently aware, but thoughts and suffering also exist.
Therefore the method is that of remaining awake but with the thoughts stilled. Ramana says this is the state of Jagrat-Sushupti, which is also the state of the Jnani (the knower of truth or the enlightened sage). Ramana states this jagrat-susupti is also called Samadhi (talks 286, 313) and that it is also Mukti (liberation, talk 311) and bliss (talks 609, 372).
I will start with an excerpt from Talk 609 as this goes into the most detail, and the opening paragraphs alone contain many gems that should be carefully contemplated on. Thereafter the talks are chronological, with bold added by myself for emphasis.
Wishing you the eternal peace that is already ever-present
From Talks with Sri Ramana Maharshi, talk 609:
The incentive to realise can arise only in the waking state and efforts can also be made only when one is awake. We learn that the thoughts in the waking state form the obstacle to gaining the stillness of sleep.
“Be still and know that I AM God”.
So stillness is the aim of the seeker. Even a single effort to still at least a single thought even for a trice goes a long way to reach the state of quiescence. Effort is required and it is possible in the waking state only. There is the effort here: there is awareness also; the thoughts are stilled; so there is the peace of sleep gained. That is the state of the Jnani. It is neither sleep nor waking but intermediate between the two. There is the awareness of the waking state and the stillness of sleep. It is called jagrat-sushupti.
Call it wakeful sleep or sleeping wakefulness or sleepless waking or wakeless sleep. It is not the same as sleep or waking separately. It is atijagrat (beyond wakefulness) or atisushupti (beyond sleep).
It is the state of perfect awareness and of perfect stillness combined. It lies between sleep and waking; it is also the interval between two successive thoughts. It is the source from which thoughts spring; we see that when we wake up from sleep. In other words thoughts have their origin in the stillness of sleep. The thoughts make all the difference between the stillness of sleep and the turmoil of waking.
Go to the root of the thoughts and you reach the stillness of sleep. But you reach it in the full vigour of search, that is, with perfect awareness. That is again jagrat-sushupti spoken of before. It is not dullness; but it is Bliss. It is not transitory but it is eternal. From that the thoughts proceed. What are all our experiences but thoughts? Pleasure and pain are mere thoughts. They are within ourselves. If you are free from thoughts and yet aware, you are That Perfect Being.
From Talks with Sri Ramana Maharshi, talk 286:
Sushupti continues in this state also. We are ever in sushupti. That should be consciously gone into and realised in this very state. There is no real going into or coming from it. Becoming aware of that is samadhi.
From Talks with Sri Ramana Maharshi, talk 290:
Bring sleep into the waking state (jagrat sushupti) and you will be all right.
From Talks with Sri Ramana Maharshi, talk 311:
The Self who was undifferentiated in sleep is differentiated in the present state, and sees the diversity. The Real Existence is the only One devoid of objective knowledge. That is absolute consciousness. That is the state of happiness, as admitted by all of us. That state must be brought about even in this waking state. It is called jagrat sushupti. That is mukti.
From Talks with Sri Ramana Maharshi, talk 313:
Take another example: A passenger in a cart has fallen asleep. The bulls move or stand still or are unyoked on the journey. He does not know these occurrences, but finds himself in a different place after he wakes up. He has been blissfully ignorant of the occurrences on the way, but his journey has been finished.
Similarly with the Self of the person. He is asleep in the body. His waking state is the movement of the bulls, his samadhi is their standing still (because samadhi = jagrat sushupti) i.e., to say, he is aware of but not attached to actions. So the bulls are in harness but do not move. His sleep is the unyoking of the bulls, for there is complete suspension of activities corresponding to the release of the bulls from the yoke.
From Talks with Sri Ramana Maharshi, talk 372:
D.: Sleep state is said to be the experience of Bliss, yet, on recollecting it the hairs do not stand on end. Why should they do so, if the samadhi state is recollected?
M.: Samadhi means sleep in waking state (jagrat sushupti). Bliss is overpowering and the experience is very clear, whereas it is different in sleep.
From Talks with Sri Ramana Maharshi, talk 601:
Someone: The limitation (upadhi) of being a man cannot be got rid of.
M.: How were you in deep sleep? There was no thought of being a man.
Another: So, the state of sleep must be brought about even when one is awake.
M.: Yes. It is jagrat-sushupti.