Agatasatru said: 'When this man was thus asleep, then the intelligent person (purusha), having through the intelligence of the senses (pranas) absorbed within himself all intelligence, lies in the ether, which is in the heart. When he takes in these different kinds of intelligence, then it is said that the man sleeps (svapiti). Then the breath is kept in, speech is kept in, the ear is kept in, the eye is kept in, the mind is kept in.

In plain words: Agatasatru explains that during sleep, the knowing self gathers in the powers of all the senses and rests in the space inside the heart. Then breath, speech, hearing, sight and mind are all drawn inward. This drawing in is what we call sleep.