Read more about Health and Healing from the works of the Mother and Sri Aurobindo.
What is Health and Healing?
Good health is the exterior expression of an inner harmony. 
It is good health, a solid body, well poised when one sleeps well, eats well. When one is quite calm, well balanced, very quiet, one has a solid basis and can receive a large number of forces. 
Misconceptions of Health and Healing
Medicines has a part truth behind it—with its advantages and disadvantages. As all religions and philosophies point to the Supreme but each in a different direction, so all medical fashions are ways to health—though they don't always reach it. 
Illnesses do not come from yoga. Yoga helps to build up a health that is robust and unfailing. 
What Health and Healing is in Different Parts of Being?
To whatever cause an illness may be due, material or mental, external or internal, it must, before it can affect the physical body, touch another layer of the being that surrounds and protects it. This subtler layer is called in different teachings by various names,—the etheric body, the nervous envelope. It is a subtle body and yet almost visible. In density something like the vibrations that you see around a very hot and steaming object, it emanates from the physical body and closely covers it. All communications with the exterior world are made through this medium, and it is this that must be invaded and penetrated first before the body can be affected. 
If this envelope is absolutely strong and intact, you can go into places infested with the worst of diseases, even plague and cholera, and remain quite immune. It is a perfect protection against all possible attacks of illness, so long as it is whole and entire, thoroughly consistent in its composition, its elements in faultless balance.
There is a physical Nature which is perfectly harmonious, which has an absolutely harmonious working, without any disorder, without disequilibrium, without any rupture of harmony, which would be expressed, if it existed upon earth, by a perfect health, a growing force, a continuous progress; and then all that one would like to obtain from one's body one would obtain; and this can go as far as an almost unimaginable progress of perfection.
In order to be completely cured, the vital must be converted, and "to be converted" isn't to surrender—to be converted is to understand. To be converted is to adhere. 
Finally, the body obeys the mind automatically in those things in which it is formed or trained to obey it, but the relation of the body to the mind is not in all things that of an automatic perfect instrument. The body also has a consciousness of its own and, though it is a submental instrument or servant consciousness, it can disobey or fail to obey as well. 
Why is Health and Healing Important?
It is in good health that the way towards transformation is found. 
Health or illness is a choice (to express it simply). A choice of every minute. For this body, at any rate, that's how it is. 
Three powers are needed for the Divine Work: one was the power over health, the second was the power over government, and the third was the power over money.
What Happens when Health and Healing is Not Present?
Usually, unless one has taken good care to make it otherwise, the impulses—the impulses of desire—all the enthusiasms and passions with all their reactions are the masters of human life. One must already be something of a sage to be able to undergo a rigorous discipline of the body and obtain from it the ordered, regular effort which can perfect it. There is no longer any room there for all the fancies of desire. You see, as soon as one gives way to excesses, to immoderation of any kind and a disorderly life, it becomes quite impossible to control one's body and develop it normally, not to mention that, naturally, one spoils one's health and as a result the most important part of the ideal of a perfect body disappears; for with bad health, impaired health, one is not much good for anything. And it is certainly the satisfaction of desires and impulses of the vital or the unreasonable demands of certain ambitions which make the body suffer and fall ill. 
What is Illness
Illness without any exception is the expression of a break in equilibrium. Speaking only of the body, not of the nervous illnesses of the vital or of mental illnesses. That is, if all your organs, all the members and parts of your body are in harmony with one another, you are in perfect health. But if there is the slightest imbalance anywhere, immediately you get either just a little ill or quite ill, even very badly ill, or else an accident occurs. That always happens whenever there is an inner imbalance. 
An illness of the body is always the outer expression and translation of a disorder, a disharmony in the inner being; unless this inner disorder is healed, the outer cure cannot be total and permanent. 
How to Cultivate Health and Healing?
What are the Prerequisites?
Health naturally depends upon the sadhana. 
Whatever the effort, whatever the difficulty, whatever time it takes, whatever number of lives, you must know that all this doesn't matter: you KNOW you ARE the Master, that the Master and you are the same. To know it INTEGRALLY, and nothing must belie it. Health depends on their inner life (an intermediate inner life, not the deepest), it's because of this. 
If one has the healing capacity, there is the capacity to remedy wear and tear. 
For the spiritual life to give and not to demand is the rule. The sadhak however can ask for the Divine Force to aid him in keeping his health or recovering it if he does that as part of his sadhana so that his body may be able and fit for the spiritual life and a capable instrument for the Divine Work. 
How Does the Physical Healing Happen?
It readily takes in all kinds of suggestions and these can rapidly change and almost remould its condition. Depression and discouragement have a very adverse effect; they cut out holes in it, as it were, in its very stuff, render it weak and unresisting and open to hostile attacks an easy passage. 
How to Deal with Pain?
First point: do not stress the pain by telling yourself, "Oh, how painful! Oh, this pain is unbearable! Oh, it is being worse and worse, I shall never be able to bear it", etc., all this sort of thing. The more you go on thinking like this and feeling like this and the more your attention is concentrated on it, the pain increases amazingly. Second point: as I said, it depends on your habits. If you know how to concentrate, to be quiet, you try to realise within yourself a state of peace or attempt to enter into a conscious contact with a force of peace. Suppose you succeed more or less completely. Then, if you can draw the peace into yourself and bring it down into the solar plexus―for we are not talking of inner states but of your physical body―and from there direct it very calmly, very slowly I might say, but very persistently, towards the place where the pain is more or less sharp, and fix it there, this is very good. But if by widening this movement you can add a sort of mental formation with a little life in it―if by my aspiration, my concentration, I can bring into the cells of the body the consciousness of this sole Reality, all disorder must necessarily cease… 
To separate yourself from the thing and call in the Mother's force to cure it [is the Yogic method]—or else to use your own will force with faith in the power to heal, having the support of the Mother's force behind you. If you cannot use either of these methods then you must rely on the action of the medicine. 
Remain quiet, within, concentrated only on receiving strength and health, confident that the Divine is with you all the time, and you will soon be all right. 
It depends on the part. The method is almost the same for all parts of the being. To begin with, the first condition: to remain as quiet as possible. You may notice that in the different parts of your being, when something comes and you do not receive it, this produces a shrinking—there is something which hardens in the vital, the mind or the body. There is a stiffening and this hurts, one feels a mental, vital or physical pain. So, the first thing is to put one's will and relax this shrinking, as one does a twitching nerve or a cramped muscle; you must learn how to relax, be able to relieve this tension in whatever part of the being it may be. 
It must be an integral faith and it must be absolute. And it must be of the right kind, not merely a force of mental thought or will, but something more and deeper. 
Knowledge, when it goes to the root of our troubles, has in itself a marvellous healing-power as it were. As soon as you touch the quick of the trouble, as soon as you, diving down and down, get at what really ails you, the pain disappears as though by a miracle. Unflinching courage to reach true knowledge is therefore the very essence of yoga. No lasting superstructure can be erected except on a solid basis of true Knowledge. 
Through Calm Presence
Suppose there is a pain, some sign or other that something in the body is out of order. In the consciousness—in the consciousness—you are absolutely indifferent, which means that whether it's life or death, disease or health, there is equality; but if the body reacts according to its old habit, "What should be done to get over it?" If, on the other hand, the cells have learned their lesson and say right away, "Lord, Your presence" (without words—the attitude), pfft! the thing goes. 
You cannot imagine the immense flood of force that is at your disposal! And generally you do not feel it even. 
When one has a thought, a well-made mental formation which goes out of you, it becomes an independent entity and continues on its way and it does that for which it was made. It continues to act independently. That is why one must be on your guard. If one have made such a formation and it has gone out, it has gone out to do its work; and after a time one finds out that it was perhaps not a very happy thing to have a thought like that, that this formation was not very beneficial; now that it has gone out, it is very difficult for you to get hold of it again. One must have considerable occult knowledge. It has gone out and is moving on its way…
Through Sincerity and Aspiration
One must sincerely want to be healed, for otherwise it does not work. If one wants to have the experience solely for the experience's sake and then the next minute one returns to what one was before, this does not work. 
Overreliance on Medical Science
No external measure can enable us to react against the harm caused by mental faith in the necessity of drugs. 
Read more about Health and Healing from the works of the Mother and Sri Aurobindo.