When the mind and body get tired due to today's activities, and withdraw themselves from their respective objects, it is called as Nidra.
Production of Sleep: The increase in Tamas results in sleep. And increase in Sattva Guna results in awakening.
Relation of Sleep with Health: Comfortable bed, proper time are important factors responsible for proper sleep. It results in nourishment, health, strength, knowledge and longevity.
Relationship Between Nourishment and Malnutrition: Night awakening results in dryness of the body, day sleep leads to unctuousness, obesity, coating and obstruction in channels and sleeping in the sitting posture does not induce dryness or unctuousness.