Bhashya
अथ यदा सुषुप्तो भवति— यदा स्वप्न्यया चरति,तदाप्ययं विशुद्ध एव; अथ पुनः यदा हित्वा दर्शनवृत्तिंस्वप्नं यदा यस्मिन्काले सुषुप्तः सुष्ठु सुप्तः संप्रसादं स्वाभाव्यंगतः भवति— सलिलमिवान्यसंबन्धकालुष्यं हित्वा स्वाभा-व्येन प्रसीदति ।कदा सुषुप्तो भवति ? यदा यस्मिन्काले, नकस्यचन न किंचनेत्यर्थः, वेद विजानाति; कस्यचन वाशब्दादेः संबन्धिवस्त्वन्तरं किंचन न वेद— इत्यध्याहार्यम्;पूर्वं तु न्याय्यम्, सुप्ते तु विशेषविज्ञानाभावस्य विवक्षित-त्वात् ।एवं तावद्विशेषविज्ञानाभावे सुषुप्तो भवतीत्युक्तम्;केन पुनः क्रमेण सुषुप्तो भवतीत्युच्यते— हिता नामहिता इत्येवंनाम्न्यो नाड्यः सिराः देहस्यान्नरसविपरिणाम-भूताः, ताश्च, द्वासप्ततिः सहस्राणि-द्वे सहस्रे अधिके सप्त-तिश्च सहस्राणि- ता द्वासप्ततिः सहस्राणि, हृदयात्-हृदयंनाम मांसपिण्डः- तस्मान्मांसपिण्डात्पुण्डरीकाकारात्, पु-रीततं हृदयपरिवेष्टनमाचक्षते- तदुपलक्षितं शरीरमिह पुरी-तच्छब्देनाभिप्रेतम्- पुरीततमभिप्रतिष्ठन्त इति-शरीरं कृ-त्स्नं व्याप्नुवत्यः अश्वत्थपर्णराजय इव बहिर्मुख्यः प्रवृत्ताइत्यर्थः ।तत्र बुद्धेरन्तःकरणस्य हृदयं स्थानम् ; तत्रस्थबुद्धि-तन्त्राणि च इतराणि बाह्यानि करणानि ; तेन बुद्धिः कर्मव-शात् श्रोत्रादीनि ताभिर्नाडीभिः मत्स्यजालवत् कर्णशष्कुल्या-दिस्थानेभ्यः प्रसारयति ; प्रमार्य च अधितिष्ठति जागरित-काले ; तां विज्ञानमयोऽभिव्यक्तस्वात्मचैतन्यावभासतयाव्याप्नोति ; संकोचनकाले च तस्याः अनुसंकुचति ; सोऽस्यविज्ञानमयस्य स्वापः ; जाग्रद्विका सानुभवो भोगः ; बुद्धयुपा-धिस्वभावानुविधायी हि सः, चन्द्रादिप्रतिबिम्ब इव जलाद्य-नुविधायी ।तस्मात् तस्या बुद्धेः जाग्रद्विषयायाः ताभिःनाडीभिः प्रत्यवसर्पणमनु प्रत्यवसृप्य पुरीतति शरीरे शेतेतिष्ठति- तप्तमिव लोहपिण्डम् अविशेषेण संव्याप्य अग्नि-वत् शरीरं संव्याप्य वर्तत इत्यर्थः ।स्वाभाविक एव स्वा-त्मनि वर्तमानोऽपि कर्मानुगतबुद्ध्यनुवृत्तित्वात् पुरीतति शेत इत्युच्यते ।न हि सुषुप्तिकाले शरीरसंबन्धोऽस्ति ।' तीर्णो हि तदा सर्वाञ्छोकान्हृदयस्य ' इति हि वक्ष्यति ।सर्वसंसारदुःखवियुक्तेयमवस्थेत्यत्र दृष्टान्तः- स यथा कुमारो वा अत्यन्तबालो वा, महाराजो वा अत्यन्तवशप्रकृतिः यथोक्तकृत्, महाब्राह्मणो वा अत्यन्तपरिपक्वविद्याविनयसंपन्नः, अतिघ्नीम्- अतिशयेन दुःखं हन्तीत्यतिघ्नी आनन्दस्य अवस्था सुखावस्था ताम् प्राप्य गत्वा, शयीत अवतिष्ठेत ।एषां च कुमारादीनां स्वभावस्थानां सुखं निरतिशयं प्रसिद्धं लोके ; विक्रियमाणां हि तेषां दुःखं न स्वभावतः ; तेन तेषां स्वाभाविकावस्था दृष्टान्तत्वेनोपादीयते, प्रसिद्धत्वात् ; न तेषां स्वाप एवाभिप्रेतः, स्वापस्य दार्ष्टान्तिकत्वेन विवक्षितत्वात् विशेषाभावाच्च ; विशेषे हि सति दृष्टान्तदार्ष्टान्तिकभेदः स्यात् ; तस्मान्न तेषां स्वापो दृष्टान्तः- एवमेव, यथा अयं दृष्टान्तः, एष विज्ञानमय एतत् शयनं शेते इति- एतच्छब्दः क्रियाविशेषणार्थः- एवमयं स्वाभाविके स्व आत्मनि सर्वसंसारधर्मातीतो वर्तते स्वापकाल इति ॥
In plain words
Consider what happens when a person falls into deep sleep. Even while he is still moving about in a dream, something in him is already pure. Then, further still, when he lets go of the very act of seeing dreams — whenever that moment comes, he is in deep, sound sleep, settled into calm, into his own natural state. It is like water: once it lets go of the cloudiness that came from mixing with something else, it clears on its own. So when exactly is someone in deep sleep? Whenever he knows nothing — truly nothing at all. (Some would read this more narrowly, as meaning only that he perceives no outside object — but that's not the real point; the real point is that ALL specific knowing has stopped. That is what deep sleep is meant to show us.) So far, then: deep sleep is simply the absence of any particular knowing. But how, exactly, does someone arrive there? Here is how: there are channels in the body called the Hitā — the veins — formed out of the body's own digested food. There are seventy-two thousand of them, running out from the heart. (By 'heart' here we mean the physical lump of flesh, shaped like a lotus bud.) The membrane wrapped around that lump of flesh is called the purītat, and it's this — the body defined by that covering — that scripture means when it says these channels 'rest in the purītat': they spread through the whole body, facing outward, the way veins fan out across a peepal leaf. Now, the heart is where the intellect — the inner instrument of the mind — actually sits; every other organ is just its outward tool. Carried by old habit, the intellect reaches out through those very channels — like a fisherman's net cast wide — all the way to the ears and the other sense-openings, and once it has spread itself out, it stays in charge of them all day, through waking life. And it's the awareness-self that lights up that whole network, the way its own consciousness shines through it. When that network contracts — when a person falls asleep — the awareness-self withdraws along with it. That withdrawal IS what we call this self's 'sleep'; what happens during waking, by contrast, is 'experience.' It simply takes on the shape of whatever the intellect happens to be, the way a reflection of the moon takes the shape of whatever water it falls on. So, following that same withdrawal of the intellect — the very intellect that had been reaching out toward the waking world — back along those channels, the self comes to rest in the purītat, in the body: meaning, it pervades the whole body evenly, the way heat pervades a heated ball of iron. Even though, in truth, this self never leaves its own nature for a moment, we still say it 'lies in the purītat' simply because it goes along with the karma-driven intellect. In deep sleep there is, in truth, no real connection to the body at all — as we'll hear later: 'then, he has crossed beyond every sorrow of the heart.' Here's a picture of that state — completely free of every sorrow that comes with being caught in the world: think of a young prince, or any small child, or a mighty king whose people obey his every word, or a great brahmin steeped fully in learning and grace. Each of them, on reaching that state — called 'atighnī' because it utterly destroys suffering, a state of pure bliss — simply lies down and rests in it. And everyone knows: when people like this are in their natural state, their happiness has no equal; whatever unhappiness they show only comes from being disturbed out of it, never from who they really are. That is exactly why their natural, undisturbed state — and not their literal act of sleeping — is what's being pointed to here. Their sleep as such isn't the point of comparison at all; only their untroubled bliss is. If we pushed the comparison any further than that, the illustration and the thing it's illustrating would start to pull apart. So: it isn't their sleep that serves as the image — it's their happiness. In exactly the same way, when scripture says 'this awareness-self sleeps this sleep,' that little word 'this' isn't naming some object — it's simply describing the manner of the sleeping. And that is exactly the point: in the very same way, this self simply rests in its own natural being, entirely beyond every condition of transmigration, during what we call sleep.
Close to the Sanskrit
Now, when he is in deep sleep — when he still moves about by means of the dream-faculty, then too this one is indeed pure; then again, when, having abandoned the dream-seeing function, at whatever time he is in deep sleep, soundly asleep, having gone to tranquility, to his own natural state — [it is] as when water, having abandoned the turbidity caused by contact with other things, settles by its own nature. When is he in deep sleep? At whatever time — 'of anyone, of anything' — that is, 'nothing at all' — is the meaning — he knows; or, alternatively: he knows no other substance whatsoever connected with sound, etc. — this [second reading] is to be supplied as an option; but the former is the sound one, since, in sleep, what is meant to be conveyed is the absence of all particular cognition. Thus, so far, it has been said that he is in deep sleep when there is an absence of particular cognition; but by what process does he come to be in deep sleep? This is now explained: those channels named 'Hitā' — the veins — are a transformation-product of the body's food-essence; and they number seventy-two thousand — two thousand plus seventy more thousand — that is, seventy-two thousand; from the heart — 'heart' meaning the lump of flesh — from that lotus-shaped lump of flesh, [scripture] calls the encasement of the heart 'purītat'; the body characterized by that is here meant by the word 'purītat' — [as in] 'they stand fixed in the purītat' — meaning that, pervading the entire body, like rows of veins in a peepal leaf, they proceed facing outward — that is the meaning. There, the heart is the seat of the intellect, the inner instrument; and the other organs, dependent on the intellect seated there, are the external instruments. By that [intellect], due to the force of past action, it extends the ear and the other [senses], by means of those channels, like a fishing net, out to the cavities of the ears and other such locations; and having spread them out, it presides over them during the waking state; that [network] the cognitive self pervades by the manifest shining-forth of its own consciousness; and at the time of contraction, it contracts along with it; that is this cognitive self's 'sleep'; the corresponding waking experience is 'enjoyment.' For it conforms to the nature of the intellect, its limiting adjunct, just as a reflection of the moon, etc., conforms to water, etc. Therefore, following the withdrawal of that intellect whose object is the waking world, by those very channels, having withdrawn along with it, [the cognitive self] lies, rests, in the purītat, in the body — meaning that, pervading the entire body uniformly, like a heated iron ball [pervaded by fire], it continues pervading the body, like fire; that is the meaning. Though it is, by its very nature, ever present in its own self, because it conforms to the intellect bound up with past action, it is said to 'lie in the purītat.' For indeed, there is no [real] connection with the body at the time of deep sleep — as it will be said: 'for then he has crossed over all the sorrows of the heart.' As for this state being disjoined from all the sorrow of transmigration — here is an illustration: just as a young prince, or an utter child, or a great king whose subjects are wholly submissive, doing exactly as commanded, or a great brāhmaṇa fully ripened in learning and discipline, having reached the state called 'atighnī' — 'atighnī' meaning that which exceedingly destroys sorrow, the state of bliss, the state of happiness — would lie down, would rest. And of these — the prince and the rest — in their natural state, the happiness is unsurpassed, well known in the world; but their sorrow, when disturbed, does not come from their own nature. Therefore their natural state is taken as the illustration, because it is well known; it is not their sleep, as such, that is meant, because what is intended by way of the illustration is [their state of untroubled bliss], and no further, detailed resemblance is intended — for if such a detailed resemblance were intended, there would result a [breakdown of the] distinction between illustration and thing illustrated. Therefore their sleep, as such, is not the illustration. In just the same way — just as this is the illustration — 'this cognitive self sleeps this sleep': here the word 'this' has the force of qualifying the manner of the action; in just this way, this self abides in its own natural self, transcending all the conditions of transmigration, at what is called the time of sleep.