Why Does Manas, Which Continuously Discerns and Deliberates, Require Sleep?

Sleep serves to restore the physical body's energy, eliminate physical fatigue, and enable the six consciousnesses to function more effectively and efficiently. The mental faculty (manas) regards the physical body as its own, considers the six consciousnesses as its own, views the five aggregates and eighteen elements as its own, and relies on the eighth consciousness to instantaneously perceive the condition of the physical body. The activities of the six consciousnesses consume energy; to reduce this energy consumption, the mental faculty decides to cease the activities of the six consciousnesses, actively shutting down their discernment of the six sense objects. It no longer wishes to perceive the six sense objects, relying solely on its own awareness. As energy continuously accumulates and vitality is restored to a certain level, the mental faculty decides to awaken, re-engage with the sensory realm, and resume the activities of the five aggregates.

If the physical body becomes fatigued, sleep is necessary to restore energy. The mental faculty then decides to sleep, preventing the six consciousnesses from continuing their activities. The mental faculty itself seeks to shut off the six sense objects and cease perceiving them, causing the five sense consciousnesses and the mental consciousness to gradually subside. Therefore, it is not the mental faculty that requires sleep, but the physical body that needs rest to replenish energy and restore vitality. This is precisely the result of the mental faculty's constant mental scrutiny. However, sleep does not affect the mental faculty's constant scrutiny; it can continue its mental processing during sleep and can even manifest dreams, engaging in mental processing within the dream state.