Subsection 7 Sleeping and waking as causes

What I said earlier of exercise I may now repeat of sleep. Nothing is better than moderate sleep, nothing worse when taken to extremes or at the wrong time. It is an accepted opinion that a melancholy person cannot sleep too much: “Sleep beyond measure is beneficial,” as though it were the sole antidote, and nothing harms them more or causes this illness sooner than wakefulness. Yet in some cases sleep may do more harm than good: in that phlegmatic, swinish, cold and sluggish melancholy of which Melanchthon speaks, which thinks of waters and spends most of its time sighing, and so on.

Too much sleep dulls the spirits and senses, fills the head with thick humours, causes downward flows of fluid and rheums, and a great accumulation of waste matter in the brain and all other parts, as Fuchs says of those who sleep like so many dormice.

Or if sleep is taken by day, on a full stomach, when the body is poorly prepared for rest, or after foods that are hard to digest, it increases frightening dreams, nightmare oppression, sleepwalking, cries in the night and great restlessness. Such sleep, as one writer observes, predisposes the body to many dangerous diseases.

But, as I have said, excessive wakefulness is both a symptom and a common cause. It dries the brain, causes frenzy and mental derangement, and makes the body dry, thin, hard and ugly to behold, as Lemnius puts it. It corrupts the brain’s balance, burns the humours, makes the eyes sink into the head, increases choler and inflames the whole body.

And, as may be added from Galen’s On the Preservation of Health, book 3, and Avicenna, 3.1, it destroys the natural heat, produces undigested matter, impairs digestion—and what does it not do? With good reason, then, Crato, consultation 21, book 2; Hildesheim, collection 2, On Delirium and Mania; Iacchinus; Arculanus on Rhazes; Guianerius; and Mercurialis list excessive wakefulness among the principal causes.