Verse 4.6

स यदा तेजसाऽभिभूतो भवति । अत्रैष देवः स्वप्नान्न पश्यत्यथ तदैतस्मिञ्शरीर एतत्सुखं भवति ॥ ६ ॥

sa yadā tejasā'bhibhūto bhavati | atraiṣa devaḥ svapnānna paśyatyatha tadaitasmiñśarīra etatsukhaṃ bhavati || 6 ||

6. When it is overpowered with light, then this mind sees no dreams; thus then, the bliss arises in this body.

Shankara’s Commentary:

Com.—When the Dêvâ, i.e., the mind, becomes overpowered, i.e., has all the outlets of these impressions closed by the light (lodged in the nerve) known as Pitta and pertaining to the sun, then the rays, i.e., the tendencies of the mind, become absorbed into the heart along with the senses. When the mind, like fire in a log of wood, pervades the whole body in its form, as general knowledge (as opposed to a special modification) then he sleeps. All that time, this Dêvâ named mind, does not see dreams, the door of vision being closed by light. Then, in this body, this bliss arises, which is knowledge unimpeded, pervading all body without distinction and clear.