Sleep is very similar to rest, and wakefulness is very similar to movement, but both states, in addition, have their own characteristics that we need to consider.
We say: sleep strengthens all natural forces, retaining the innate warmth, and weakens the spiritual forces, moistening and relaxing the passages of the spiritual pneuma; the pneuma substance becomes cloudy in these passages, and its soluble particles are retained there. However, sleep eliminates all types of fatigue and retards excessive evacuation; the fact is that movement increases the fluidity of matters capable of flowing, except for that which is near the skin; sleep sometimes even helps to expel it, retaining the warmth inside and distributing nutrients in the body so that what is close to the skin rushes towards it and what is far from it is retained. However, being awake is more effective in this regard, although sleep makes you sweat more than staying awake. The fact is that sleep causes perspiration by completely capturing the juices, and not by constant easy dissolution. Whoever sweats often in a dream without any other reason for it means that he is so full of food that he cannot bear it. If sleep finds matter ready to be digested or ripened, it turns it into blood essence and heats it. The heat dissipates throughout the body, and the body warms up from its innate warmth. If sleep finds hot bile juices and continues for a long time, then the body warms up from extraneous warmth. When sleep finds emptiness, it cools the body by dissolving the juices, and if it finds juices that do not obey the digestive force, it cools it by spreading them.
Wakefulness produces actions that are the opposite of all this, but when it becomes excessive, it spoils the nature of the brain, giving it a certain dryness, and weakens it, producing insanity; excessively long vigil burns juices and causes acute illnesses.
And excessive sleep produces the opposite of all this. It gives rise to sluggishness of mental strength, dullness of the brain and cold illnesses, and this happens because sleep prevents the dissolution of the juices. Wakefulness increases appetite and hunger, as it dissolves matter and weakens digestion, reducing digestive power. Tossing in bed between wakefulness and sleep is the worst of all conditions.
The predominant property of the sleep state is that the warmth in sleep goes inward, and the cold comes out; therefore people need a covering for all their members, which is not necessary for the waking person. In the following books you will find many discussions about the influence of sleep and the circumstances associated with sleep.