唯識二十論述記 2.268

2.268

述曰：釋上句頌。不定四中，睡眠心所能令有情身分沈重，心分惛昧，在寐夢心，為此所壞，令心昧故，慮不分明，勢力羸劣。其覺時心，既無眠壞，緣境明了，勢力增強，不同夢位。其狂、醉等，為緣壞心，羸劣亦爾。此但答問如夢位心。

Commentary: This explains the first line of the verse. Among the four indeterminate [mental factors], the sleep caitta can cause a sentient being's bodily constituents to become heavy and the mental constituents to become dull; the mind in a sleep-dream is impaired by this, and because it makes the mind dull, its deliberation is not distinct and its power is feeble and inferior. As for the waking mind, since it is not impaired by sleep, it apprehends objects clearly and its power is increased and strong, unlike in the dream state. In madness, intoxication, and the like, the mind impaired by conditions is similarly feeble and inferior. This merely answers the question regarding the mind in the dream state.