Of the blessings of those who fall sick is that sickness is one of the strongest and most powerful antidotes to the sins that we commit. There is hardly anything that will expiate our sins that is more powerful than trials and afflictions that befall us.
Allah says:
'And whatever strikes you of disaster – it is for what your hands have earned; but He pardons much.' (Surah ash-Shuraa, 30)
Every sickness and calamity that happens: a death of a loved one, a loss of a relative, financial economic, distress physical hardship, a fever, any type of pain and suffering.
Source: Aboutislam