The most important thing during illness is to offer to God patience and thanksgiving for His merciful visitations. Sickness purifies sins and gives one time to meditate on the past.
As long as the flesh is in full health, let us observe abstinence at all times and in every place. When it has been tamed (which I do not suppose is possible this side of the grave), then let us hide our accomplishment.
Accordingly, a man will neither be puffed up through pride, nor cast down by despair, if he uses the good things divinely bestowed on him, to the glory of the Giver; withholding his desires from the things which he knows will hurt him. And so he that would preserve himself from the wickedness of envy, from the corruption of sensuality, from the unrest of anger, from the desire of revenge, will be purified by the sanctifying power of true abstinence, and will taste the joy of imperishable delights, so that by making spiritual use of them, he will learn to change earthly possessions into heavenly, not by storing what he has received, but by multiplying more and more that which he has been given.
The experience of the ages shows that the sign of the cross has great power over all a person’s actions during the entire course of his life. Therefore it is necessary to strive to root in children the habit of protecting themselves with the sign of the cross often, especially when receiving food and drink, going to bed and waking up, before departing somewhere in a vehicle, before leaving and entering any place; and they should not make the sign carelessly or according to fashion, but precisely, beginning with the forehead to the solar plexus, then to both shoulders, so that a proper cross is produced.... The sign of the cross has saved many from great dangers and afflictions.
Just as we must beware of overeating, so too we must beware of excessive temperance or abstinence. Excessive temperance weakens the body, destroys wakefulness, coolness and freshness which are indispensable for vigilance, and which fade and weaken when the physical powers succumb and fail. If you force a weak body to labor beyond its powers, you subject your soul to double darkness, and lead it into confusion (and not relief)...
Pray before your body takes rest on your bed... If you are tempted, make the Sign (of the Cross) on your forehead reverently… for this is a known and tested weapon against the Devil.
Stint your stomach and you will certainly lock your mouth, because the tongue is strengthened by an abundance of food. Struggle with all your might against the stomach and restrain it with all sobriety. If you labor a little, the Lord will also soon work with you.