I wanted to pass along this gem from Evagrius of Pontus, a fourth-century Christian whose life took him from his native Cappadocia (where he was friends with Basil of Caesarea and a close associate of Gregory of Nazianzus) to the desert of Egypt. He fled to the desert to avoid temptation after falling in love with a married woman. Also, he had trouble staying awake while reading.
“There are certain impure demons who always sit in front of those engaged in reading and try to seize their mind, often taking pretexts from the divine scriptures themselves and ending in evil thoughts. It sometimes happens that they force readers to yawn more than they are accustomed and they instill a very deep sleep quite different from usual sleep. Whereas some of the brothers have imagined that it is in accordance with an unintelligible and natural reaction, I for my part have learned this by frequent observation; they touch the eyelids and the entire head, cooling it with their own body for the bodies of the demons are very cold and like ice; and the head feels as if it is being sucked by a cupping glass with a rasping sound. They do this in order to draw to themselves the heat that lies within the cranium, and then the eyelids, relaxed by the moisture and cold, slip over the pupils of the eyes. Often in touching myself I have found my eyelids fixed like ice and my entire face numb and shivering. Natural sleep however normally warms bodies and renders the faces of healthy people rosy, as one can learn from experience itself. But the demons provoke unnatural and prolonged yawning, and they make themselves small enough to touch the interior of the mouth.”
From On Thoughts, chapter 33.