Sickness and Pain are a gift of God:

In the Kalyva of Saint Chrysostomos of the Skete of Koutloumousiou of the Monastery of Saint Panteleimon on Mount Athos, there lived years ago Monk Daniel who for 20 years was sick and had headaches and backaches, kidney and heart problems, leg problems and pain sometimes throughout his entire body. 

Many times he travelled to doctors and received numerous X-ray examinations and radiographies, but the outcome was always the same. The doctors could not find any physical explanation for his sickness. Yet Monk Daniel continued to suffer his sicknesses and there was not a physician or scientist to be found that could help him.

One 27th of July, during the vigil of Saint Panteleimon, brother Daniel prayed with tears in his eyes and pleaded with Saint Panteleimon saying: "Saint of God and protector of our Skete, you who are a physician and for the love of Christ was martyred and spilled your blood, show your love and plead to the Master Christ to grant me health, so that with health I could glorify His name and psalmodize during the vigils."

Having said this, Monk Daniel grew a bit tired and took some sleep. He then in a vision saw Saint Panteleimon kneeling before the throne of God pleading for the health of Daniel. Monk Daniel heard the Master Christ say to Saint Panteleimon: "My brother Great-Martyr Panteleimon, do you think you are more compassionate than me? Do you think you love humanity more than me? I understand that out of love for me you spilled your blood, but did I not also spill mine and daily spill my blood for the salvation of people's souls? Learn that it is my will in which it happens many times for the body to suffer in order for the soul to be saved. This is how I want many people to be saved."

When brother Daniel heard this he awoke and glorified the name of God, thanked Saint Panteleimon for his effort and mediation, and immediately, as the same monk related, a great burden was lifted off of him and related that we must endure with patience, joy and thanksgiving the cross and situation of our sicknesses.

Source: Mystagogy