Verse 6.15.1

पुरुषं सोम्योतोपतापिनं ज्ञातयः पर्युपासते जानासि मां जानासि मामिति तस्य यावन्न वाङ्मनसि सम्पद्यते मनः प्राणे प्राणस्तेजसि तेजः परस्यां देवतायां तावज्जानाति ॥ ६.१५.१ ॥

puruṣaṃ somyotopatāpinaṃ jñātayaḥ paryupāsate jānāsi māṃ jānāsi māmiti tasya yāvanna vāṅmanasi sampadyate manaḥ prāṇe prāṇastejasi tejaḥ parasyāṃ devatāyāṃ tāvajjānāti || 6.15.1 ||

1. When a person is seriously ill, O Somya, his relatives sit around him and ask: ‘Do you recognize me? Do you recognize me?’ So long as his speech does not merge with his mind, his mind with his prāṇa, his prāṇa with the heat in his body, and the heat with the Supreme Self, he will be able to recognize them.

Word-for-word explanation:

Puruṣam, a person; uta, also; somya, O Somya; upatāpinam, who is sick; jñātayaḥ, relatives; pari-upāsate, sit around him; jānāsi mām jānāsi mām iti, saying ‘Do you recognize me, do you recognize me?’; yāvaṭ, so long as; tasya, his; vāk, speech; manasi na sampadyate, does not merge in his mind; manaḥ prāṇe, the mind into prāṇa; prāṇaḥ tejasi, prāṇa into heat; tejaḥ parasyām devatāyām, heat into the Supreme Deity; tāvat jānāti, that long he knows [them].

Commentary:

The Upaniṣad has previously said that from the Self comes heat, from heat comes prāṇa (the life force), from prāṇa comes the mind, and from the mind comes speech. Then at the time of death, these things go back in the reverse order—speech goes back into the mind, etc. The resting place is the Self, Pure Spirit. Everything goes back there, and everything comes from there.

When a person is dying, it is common for his relatives to gather round and ask the person, ‘Do you recognize me?’ How long does he recognize them? So long as heat has not left the body. Even though his breathing has stopped, as long as the body is warm, the person is still alive.