Saint John of the Ladder on sleep, prayer, and psalm-singing in church

Sleep is a particular state of nature, an image of death, inactivity of the senses. Sleep is one, but, like desire, its sources and occasions are many: that is to say, it comes from nature, from food, from demons, or perhaps, sometimes, from extreme and prolonged fasting, through which the flesh is weakened and at last longs for the consolation of sleep.