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Tattva Bodhaतत्त्वबोधः
Tattva Bodha · passage 21

Deep sleep

अतः सुषुप्त्यवस्था का? अहं किमपि न जानामि सुखेन मया निद्राऽनुभूयत इति सुषुप्त्यवस्था । कारणशरीराभिमानी आत्मा प्राज्ञ इत्युच्यते ।
ataḥ suṣuptyavasthā kā? ahaṃ kimapi na jānāmi sukhena mayā nidrā'nubhūyata iti suṣuptyavasthā | kāraṇaśarīrābhimānī ātmā prājña ityucyate |

Then what is the deep-sleep state? 'I knew nothing at all; I slept in ease.' That recollection is the deep-sleep state. The Self, taking the causal body as itself, is called prājña.

In plain words

What, then, is the deep-sleep state (suṣupti)? It is the state recalled as, 'I knew nothing; I slept happily.' The Self, identifying with the causal body, is here called prājña.

The terms set down here
  • suṣupti