please explain what happens to our body or what is the difference between deep sleep and death? (as mentioned in vedas or upanishads or any of our Hindu literature)
Difference between Deep sleep and Death!
Death is when the soul leaves the body, and deep sleep is when the Jiva resides in Brahman in the body as this question and answer shows.
6.8 - Uddalaka the son of Aruna said to his son Svetaketu: "Learn from me, my dear, the true nature of sleep. When a person has entered into deep sleep, as it is called, then, my dear, he becomes united with Pure Being (Sat), he has gone to his own Self. That is why they say he is in deep sleep (svapiti); it is because he has gone (apita) to his own (svam).
In deep sleep, the Jiva doesn't leave the body, but resides somewhere in the heart or nerves.
Regarding death, the Bhagavad Gita says:
2.13 - Just as the embodied Self passes through childhood, youth and old age [pertaining to that body], so [at death] it passes into another body. A wise man is not confused thereby.
Dreamless Sleep and Death as explained in Brihadaranyaka Upanishad
4.3.17. After enjoying himself and roaming in the waking state, and merely seeing (the results of) good and evil, he comes back in the inverse order to his former condition, the dream state (or that of profound sleep).
As a great fish swims alternately to both the banks (of a river), eastern and western, so does this infinite being move to both these states, the dream and waking states.
As a hawk or a falcon flying in the sky becomes tired, and stretching its wings, is bound for its nest, so does this infinite being run for this state, where falling asleep he craves no desires and sees no dreams.
That is his form—beyond desires, free from evils, and fearless. As a man, fully embraced by his beloved wife, does not know àṅything at all, either external or internal, so does this infinite being (self), fully embraced by the Supreme Self, not know anything at all, either external or internal. That is his form—in which all objects of desire have been attained and are but the self, and which is free from desires and devoid of grief
In this state a father is no father, a mother no mother, the worlds no worlds, the gods no gods, the Vedas no Vedas. In this state a thief is no thief, the killer of a noble Brāhmaṇa no killer, a Caṇḍāla no Caṇḍāla, a Pulkasa no Pulkasa, a monk no monk, a hermit no hermit. (This form of his) is untouched by good work and untouched by evil work, for he is then beyond all the woes of his heart (intellect).
Similar explanation about dreamless sleep is also present in Chapter 1, Shiva Geeta (Padma Purana). About Death
4.4.3. Just as a leech supported on a straw goes to the end of it, takes hold of another support and contracts itself, so does the self throw this body aside—make it senseless—take hold of another support, and contract itself.
That self is indeed Brahman, as well as identified with the intellect, the Manas and the vital force, with the eyes and ears, with earth, water, air and the ether, with fire, and what is other than fire, with desire and the absence of desire, with anger and the absence of anger, with righteousness and unrighteousness, with everything—identified, as is well known, with this (what is perceived) and with that (what is inferred). As it does and acts, so it becomes; by doing good it becomes good, and by doing evil it becomes evil—it becomes virtious through good acts and vicious through evil acts. Others, however, say, ‘The self is identified with desire alone. What it desires, it resolves; what it resolves, it works out; and what it works out, it attains.’
Regarding this there is the following verse: ‘Being attached, he, together with the work, attains that result to which his subtle body or mind is attached. Exhausting the results of whatever work he did in this life, he returns from that world to this for (fresh) work.’ Thus does the man who desires (transmigrate). But the man who does not desire (never transmigrates). Of him who is without desires, who is free from desires, the objects of whose desire have been attained, and to whom all objects of desire are but the Self—the organs do not depart. Being but Brahman, he is merged in Brahman.
What one thinks at the time of death, the Self takes that form. King turned sage Bharat had to take a form of deer because of end days Moha of lost deer, despite doing Tapas several years. One who is without any desires at the time of death, is absorbed back in the Self Brahman. This is also explained in Geeta Chapter 8.
Bhagavad Gita 8.5 Those who relinquish the body while remembering Me at the moment of death will come to Me. There is certainly no doubt about this.
Bhagavad Gita 8.6 Whatever one remembers upon giving up the body at the time of death, O son of Kunti, one attains that state, being always absorbed in such contemplation.
Bhagavad Gita 8.9 – 8.10 God is Omniscient, the most ancient one, the Controller, subtler than the subtlest, the Support of all, and the possessor of an inconceivable divine form; He is brighter than the sun, and beyond all darkness of ignorance. One who at the time of death, with unmoving mind attained by the practice of Yog, fixes the prāṇ (life airs) between the eyebrows, and steadily remembers the Divine Lord with great devotion, certainly attains Him.
Bhagavad Gita 8.11 Scholars of the Vedas describe Him as Imperishable; great ascetics practice the vow of celibacy and renounce worldly pleasures to enter into Him.
Bhagavad Gita 8.13 One who departs from the body while remembering Me, the Supreme Personality, and chanting the syllable Om, will attain the supreme goal.
From what I have understood, there are two kinds of deaths:
- Death of material body, when soul leaves old body and enters new body.
- Death of ego, when you become truth through meditation.
In deep sleep we are still in our bodies and ego is still there. In deep sleep mind and body regenerate. When we become self-realized, we remail fully aware even while sleeping.