Chandogya Upanishad 6.8.2

When we are sound asleep, what happens to the mind? The mind withdraws; it retires and temporarily goes back to the Self. Is this the same as samādhi, the superconscious state? Vedānta says, no, there is a distinction between samādhi and this experience of sound sleep. Both experiences bring great joy and peace, but deep sleep is only temporary. It is just for a while. We are still held by the rope of ignorance, and we do not know our real Self. When we come back from deep sleep, we are just as tightly bound as we were before we slept.

The Upaniṣad gives the example here of a bird tied to a rope, struggling to get free. It starts flying in all directions, seeking a safe place—any place, anywhere else than where it is bound. At last it must give up and return to its place of bondage.

Sri Ramakrishna used to give an illustration very similar to this. A bird is sitting on the mast of a ship and soon falls asleep. It does not notice that the ship has set sail. Finally, when the ship has gone far out to sea, it wakes up and starts looking around for land. Flying to the east, it eventually gets tired, and, not finding any land, comes back to the ship.

In the same way, it flies out to the west, to the north, and to the south, but all it sees is water everywhere. At last the bird decides to take refuge on the mast of the ship.

Swami Vivekananda says that all of us are struggling to be free. Freedom is our birthright. You are trying to be free; a student is trying to be free; a teacher is trying to be free. All of us, irrespective of our situation in life, are trying in one way or another to attain freedom.

The Upaniṣad is saying that when we are awake, we are like the bird flying in different directions. We are constantly fluttering around, doing this and doing that. Sometimes we are attracted by something here, and then again by something there. Our minds are always roaming about. But finally we get tired and surrender our minds to prāṇa—that is, we lie down and go to sleep. And if we are lucky, we have good sound sleep. The word prāṇa here means the Self.

Meister Eckhart once said that the mind has two eyes. One eye is always looking outside, looking at the things around. But the other eye is looking inside, looking and searching, as it were, into one’s own Being. Finally one discovers the ‘Castle of Security.’ What is this Castle of Security? It is the Self. When we enter into this castle we are at peace.

That is what the Upaniṣad also says here. When a person is able to retreat into his own Self, even temporarily, he attains a state of peace and joy. In deep sleep, we temporarily enter the castle. It