There is no one who in the course of a lifetime has not had to face some form of illness.
Illness is inevitably linked to the human condition. 
No organism is perfectly healthy. 
'Health' itself is never more than a balance between the forces of life and other forces that oppose them.

Christians with strong faith should seek ultimate healing from diseases in
Jesus Christ
who is the Source of all healing.

Canon for the Sick - Sessional Hymn, Tone 8   I lie on a bed of sinfulness, wounded by the passions. But as Thou didst raise Peter's mother-in-law and save the paralytic who was carried about with his bed, so do Thou now also visit mine infirmity, O Merciful One Who didst bear the infirmities of our race.  Thee alone we know to be patient and compassionate, a merciful Physician of souls and bodies, Christ our God, Who sendest sickness and again healing, Who grantest forgiveness unto them that repent of their sins, and Who alone art merciful and compassionate.

I, a sinner, lie weeping upon my bed.  Grant me pardon, O Christ God, raise me up from this sickness, and free me from the sins which I have committed from my youth.  Through the prayers of the Mother of God grant these petitions.  

Take pity and save me, raise me up from my sick-bed; for my strength within me hath failed, and I am entirely possessed by desperation.  O Christ God, heal me who am grievously ill, for Thou are the Divine Physician of body and soul.  

I Have Found a Physician - Prayer of St. Ambrose - Attributed to St. Matthew at his conversion.

Thee alone I follow, Lord Jesus, Who heals my wounds.  For what shall separate me from the love of God, which is in Thee?  Shall tribulation, or distress or famine?  I am held fast as though by nails and fettered by the bonds of charity.  Remove from me, O Lord Jesus, with Thy potent sword, the corruption of my sins.  Secure me in the bonds of Thy love, cut away what is corrupt in me.  Come quickly and make an end of my many hidden and secret afflictions and vices.  Open the wound, lest the evil humor, the infection spread.  With Thy new washing, cleanse in me all that is stained.  Hear me, you earthly men, who in your sins bring forth drunken thoughts:

I have found a Physician. 

He dwells in heaven and distributes His healing on earth.  He alone can heal my pains Who Himself has none.  He alone Who knows what is hidden can take away the grief of my heart, the fear of my soul - Jesus Christ.

Christ is Grace!
Christ is Life!
Christ is Resurrection!

Your wounds do not surpass the Physician's skill. 
Have faith, tell the Physician what ails you.  - Saint Cyril of Jerusalem