BṚHADĀRAṆYAKA UPANISHAD · 2.1.19

अथ यदा सुषुप्तो भवति ।
यदा न कस्य चन वेद ।
हिता नाम नाद्यो द्वासप्ततिः सहस्राणि हृदयात् पुरीततम् अभिप्रतिष्ठन्ते ।
ताभिः प्रत्यवसृप्य पुरीतति शेते ।
स यथा कुमारो वा महाराजो वा महाब्राह्मणो वातिघ्नीम् आनन्दस्य गत्वा शयीत ।
एवम् एवैष एतच् छेते ॥

atha yadā suṣupto bhavati ।
yadā na kasya cana veda ।
hitā nāma nādyo dvāsaptatiḥ sahasrāṇi hṛdayāt purītatam abhipratiṣṭhante ।
tābhiḥ pratyavasṛpya purītati śete ।
sa yathā kumāro vā mahārājo vā mahābrāhmaṇo vātighnīm ānandasya gatvā śayīta ।
evam evaiṣa etac chete ॥

Next, when he is in profound sleep, and knows nothing, there are the seventy-two thousand arteries called Hita, which from the heart spread through the body. Through them he moves forth and rests in the surrounding body. And as a young man, or a great king, or a great Brâhmana, having reached the summit of happiness, might rest, so does he then rest.

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)