Why Is Sleep Said to Be a Hindrance?

The conscious mind is like a lamp, and the mind's nature is like light. When the mind's substance gives rise to function, the lamplight appears and illuminates all dharmas. During sleep, the five consciousnesses cease, and there is no lamplight, so the dharmas of the five sense objects and six sense objects cannot manifest. After sleep, the five consciousnesses manifest, the mind consciousness manifests, brightness appears, and the lamplight illuminates the six sense objects—this is being awake. Therefore, sleep is said to be darkness that covers the light of one's own mind. Subduing sleep and cultivating away the hindrances, meditative concentration (samādhi) manifests.