Why do we not know we are dreaming in a dream?

Who is the one who knows the dream while dreaming? Who is the one who knows sense objects while awake? Both within and outside dreams, the sixth and seventh consciousnesses possess knowing; the knowing of all dharmas relies primarily on the knowing of the sixth and seventh consciousnesses. The five sense consciousnesses can only know the five sense-object realms in waking reality, and cannot know the realms within dreams, because there are no five sense-object realms in a dream. The knowing nature of the mind consciousness is greatly related to the physical body; when the physical body is obstructed, the knowing of the mind consciousness becomes weak or ceases. For a person who has attained the four dhyānas and eight samādhis, the physical body has no obstruction, and the knowing of the mind consciousness is clear and vast; whether asleep or not, they can know with great clarity. Even if they drink many bottles of wine, they will not become drunk, for alcohol can no longer numb the central nervous system of the brain, and thus the mind consciousness is unaffected.

The knowing of the mind consciousness is also greatly related to the knowing of the manas. Generally speaking, the manas knows all dharmas; the only question is whether it knows them as they truly are. As for the portion that the manas can know as it truly is, how it can influence the mind consciousness so that the mind consciousness also knows it, and promptly processes what is known—that involves the ability to communicate between the two consciousnesses. What is called the ability to communicate is wisdom; how what the mind consciousness knows can effectively influence and guide the manas also involves the ability to communicate, that is, how good the wisdom is. Wisdom is also closely related to meditative concentration (samādhi); meditative concentration can make the mind quiet, peaceful, and steady, strengthen the capacity for contemplation, and make the power of wisdom great, so that the mutual influence between the two consciousnesses becomes great. Meditative concentration can also render the physical body unobstructed; with the physical body unobstructed, the mind consciousness has no hindrance, its knowing is keen and unimpeded, and it can effectively influence the manas. Conversely, the manas can also effectively influence the mind consciousness; the two exchange what they have, and the knowing of all dharmas becomes smooth with little hindrance.

Awake and dream being alike is a wisdom realm cultivated through practice; knowing that it is a dream and not being trapped by the dream-state is wisdom. This practice mainly refers to the cultivation of meditative concentration; meditative concentration is an indispensable link in practice—only with meditative concentration can wisdom be developed, making the knowing of the sixth and seventh consciousnesses more truthful and more in accord with principle, knowing more truly, more subtly, and more vastly. And only by removing the hindrance of sleep can profound meditative concentration arise. For a person with deeper meditative concentration, thinking is clear when awake, and in dreams there is also no delusion—just as when awake—knowing the realms without hindrance.

The knowing of ordinary people has obstructions—that is what is colloquially called lacking supernatural powers—whereas the knowing of those with supernatural powers is unobstructed, having the power of knowing others' minds, the divine eye, and so on. This is the karmic retribution of the merit of concentration and wisdom; knowing the dream while dreaming is the retribution attained by a person with excellent meditative concentration whose mind has become purified. Ji Gong the monk had the four dhyānas and eight samādhis and possessed supernatural powers; no matter how much wine he drank, his nervous system would not be affected or anesthetized, and his mind consciousness was always awake, able to observe and know all realms as they truly are. When ordinary people fall asleep, the mind consciousness ceases, and that portion of the manas's function of knowing realms by relying on the mind consciousness no longer operates; therefore, when dreaming, the manas's power of discernment is weak and it does not know it is a dream, and the solitary consciousness (mano-vijñāna-eka-citta) within the dream also has very weak discernment and likewise does not know it is a dream. But a person with cultivation, whose power of meditative concentration is strong and whose physical body is unobstructed, has clear and lucid sixth and seventh consciousnesses and thus strong discernment; while dreaming, they know it is a dream and are not deluded.

Master Kuiji had the four dhyānas and eight samādhis and possessed supernatural powers; when sleeping at night he was extremely lucid, even more lucid than ordinary people when awake, with keen sixth and seventh consciousnesses. After he had fallen asleep, when a leg of a louse fell off and it cried out in pain, Master Kuiji could hear it—this is the merit of the power of meditative concentration and supernatural power. If he could hear the louse's cry while asleep, does that mean he was not actually asleep? For ordinary people, sleep is a kind of covering that can obscure their minds so they neither see nor hear, like dead people. But for one who has eliminated the covering of sleep, very little sleep suffices to nourish the physical body; their meditative concentration will reach the first dhyāna or above, their mind is clear and lucid, their obstructions are slight or entirely absent. During sleep, the mind consciousness may not be completely severed, yet the sleep is still sufficient—this differs from ordinary people.

Especially for those with supernatural powers, their sleep is like being awake, even more lucid than ordinary people when awake. In ancient times, people skilled in martial arts also slept lightly and were highly alert. This alertness can be said to belong to the mind consciousness, but the manas truly also has alertness; its alertness is even stronger in function and effect than that of the mind consciousness, so without the manas, the functions and effects of the mind consciousness cannot be fully explained. Sleep and torpor are of the same category, both belonging to the hindrances, capable of obscuring the light of the conscious mind. Only after the hindrance of sleep is eliminated will the concentration of the first dhyāna appear. The deeper the torpor when sleeping, the poorer the meditative concentration—or the absence of it—and the heavier the hindrances; the more deluded one is in dreams, the less meditative concentration one has; the more easily one becomes drunk, the greater the obstruction of the physical body and the less meditative concentration one has. Those with deep meditative concentration can regulate the physical body well, unaffected by environmental factors, without obstructing the functioning of the six consciousnesses. Therefore the power of concentration is extremely important; even for those who do not study Buddhism or cultivate practice, if meditative concentration is well cultivated, the benefits are very great.