Mbh 12.216.1a

"'Bhishma said, "The yogin who wishes to always practise sinless Brahmacharya and who is impressed with the faults attaching to dreams should, with his whole heart, seek to abandon sleep. In dreams, the embodied soul, affected by the attributes of Passion and Darkness, seems to become possessed of another body and move and act influenced by desire.[766] In consequence of application for the acquisition of knowledge and of continued reflection and recapitulation, the yogin remains always awake. Indeed, the yogin can keep himself continually awake by devoting himself to knowledge. On this topic it has been asked what is this state in which the embodied creature thinks himself surrounded by and engaged in objects and acts? True it is that the embodied being, with its senses really suspended, still thinks itself to be possessed of body with all the senses of knowledge and of action. As regards the question started, it is said that that master of yoga, named Hari, comprehends truly how it happens. The great Rishis say that the explanation offered by Hari is correct and consistent with reason. The learned say that it is in consequence of the senses being worn out with fatigue, dreams are experienced by all creatures. (Though the senses are suspended) the mind, however, never disappears (or becomes inactive) and hence arise dreams. This is said by all to be their noted cause. As the imaginings of a person that is awake and engaged in acts, are due only to the creative power of the mind, after the same manner the impressions in a dream appertain only to the mind. A person with desire and attachment obtains those imaginings (in dreams) based upon the impressions of countless lives in the past. Nothing that impresses the mind once is ever lost, and the Soul being cognisant of all those impressions causes them to come forth from obscurity.