Sleeping and Being Awake

The physician takes care of the matter of sleeping and waking and knows the function of each in healthy and sick bodies. Thus, he should be able, according to bodies of animals, to predetermine the state of a sufficient and suitable amount [of sleep] for the preservation of health and treatment of the ill. This is because sleep is a natural thing without which man cannot retain his health; there must be a definite time for it in the natural order.

The excellent Hippocrates explains it in the sixth discourse of the book On Epidemics. He said, "Weariness, eating, sleeping, and coition all must be done planfully." Galen interpreted "planfully" as meaning the limitation of their quantities for every man, as [the amount of] sleep is found naturally for different ages of man. We say that it is the kindness of the exalted God who created sleep and rest for the animal's body in order to return to it a replacement for that which was lost from it during waking. This is because during waking the natural heat expands to the outside of the body and to other regions, and spreads with it the blood which helped it form. It is spread in the body so that the animal moves by the power of [this] heat to its activities and to obtain food for survival.

Whenever it moves, moisture is lost little by little to cause dryness. If it keeps on moving and the waking is not interrupted, then the dryness becomes excessive to its body so that it will die. For this reason, the exalted God made the times of sleeping between the times of waking. This is so that the heat is gathered during sleep inside the body and cold is outside; the organism of the animal relax, its senses abate, its actions stop, and heat begins in the digestion of food, in improvement of fluids to aid the organs.

The latter exert an attractive power and are moistened in this way. This is the opposite of losing [moisture]. With sleep, also strengthening are the retentive faculty, the altering power, and the evacuating strength. Due to the soundness of these four powers and the efficiency of their activities, the body is healthy and its functions are proper in addition to strengthening nature, sleep weakens the physical powers; the senses and faculty of reason are weak during it due to their abdication of these functions.

If this is so, then the physician must know the amount of sleep and work for each man for everyone has a natural quantity which he requires according to his complexion, his habits, his activities, his food, his age, season, and the state of the air. If one of them [i.e. sleeping and wakefulness] is not in its properly natural quantitative state and time, then it indicates divergence from bodily health. For this reason, Hippocrates said, "If sleep and sleeplessness are excessive, then the necessary amount is a bad sing." When the physician sees this, then he knows that this immoderate condition indicates disease in the brain. This is because sleep is a special state of the brain and occurs when it is cold and moderately moist. If these are excessive then they cause cold brain disease. For this reason, Galen said that sleeplessness comes from coldness of the most important sentient, the brain. When this coldness is strong and mixed with moisture, then the disease called lasir'as" occurs which is cold vertigo. When dryness is also with it, the disease is called catalepsy which is called jumud. Sleeplessness is also because of the heat of the most important sentient but this heat may be either from a particular, bad complexion or from black bile.

Hippocrates said that when sleep causes pain in any disease, it is a sign of death. When sleep is useful, it is not a sign of death. Hippocrates said also that when sleep quiets the confusion of the mind, it is a good sign. Make your decision on sleep and wakefulness according to what we have considered of their conditions and according to what the ancients said about them.

Know that when sleep follows constipation of what should be evacuated or when waking follows evacuation of what was confined, then both are dependent on the difference in the states of the mixtures in the body.

When one sleeps and he has unripe food and nutriment which is unabsorbed, it ripens it, improves absorption, heats, and moistens. If it finds the body clean and nutriment is needed, it strengthens the heat and drives moisture off. For this reason, it substitutes for the small amount of substance, the coldness of the body. When [one sleeps] and [has eaten] moderate food, the normal heat is strengthened and is very useful. When during sleep there is much material, it is difficult to ripen it; then sleep is harmful. This is also so in the beginning of abscesses in intermittent fevers. For this reason, physicians order no sleep at the beginning of an abscess.

Make use of sleep and waking according to these laws. Some ancients said that in sleep there is a similarity to death. This is because perception by the senses and discrimination by them stop; it is not possible to notice anything perceptible with them. For this reason, it is necessary for students of science and for those who seek the virtues that they not show zeal for sleep but zeal for seeking the realities of science and the virtues during their lives. Otherwise, their waking is sleeping and their life is death.