Why Is Sleep Said to Be an Obstruction (Nīvaraṇa)?

Consciousness and mind are like a lamp; the nature of mind is like the light. When the mind-body manifests its function, the lamplight appears and illuminates all dharmas. During sleep, the five sense 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 sense consciousnesses arise, the mind consciousness arises, brightness appears, and the lamplight illuminates the six sense-objects—this is being awake. Therefore, sleep is said to be darkness that covers the luminosity of one's own mind. By subduing sleep and eliminating the hindrances, meditative concentration (samādhi) manifests.