What is meant by sleep ?

THE CREATOR have made our sleep as a thing for rest & have made the night as a covering The darkness of the night is as a covering, protects us from exposure to cold or heat, so this covering gives us spiritual respite from the buffets of the material world, and from the tiring activities of our own inner exertions. The rest in sleep is supplemented by the covering of the night with which we are provided by THE CREATOR.