It has been related that Imam Ahmad visited Baqi ibn Mukhalid while he was sick and said to him:
"O' Baqi, rejoice in Allah's reward. The days of health are devoid of sickness and the days of sickness are devoid of health."
This means that during days of health one never contemplates sickness, for plans and ambitions then increase, as do hopes and desires. During days of severe sickness, however, one forgets matters that pertain to times of health; weak despair encamps itself within the sick soul, and thus hopelessness prevails. Allah, the Exalted, said:
(And if we give man a taste of Mercy from Us, and then withdraw it from him, verily! He is despairing, ungrateful. But if we let him taste good [favor] after evil [poverty and harm] has touched him, he is sure to say: 'Ills have departed from me. 'Surely, he is exultant, and boastful [ungrateful to Allah]. Except those who show patience and do righteous good deeds, those: theirs will be forgiveness and a great reward [Paradise].)
(Qur'an 11: 9-11)
Commenting on this verse, Ibn Katheer wrote:
"Allah is describing man and the base characteristic that he is the possessor of (with the exception of those believers upon whom Allah has bestowed His mercy). In general, if man is afflicted with hardship after ease, he becomes hopeless of ever seeing good in the future; he shows disdain for the past ~ as if he never experienced good days ---- and despair for the future as if he never expected succor and relief."
Analogous is his attitude when he experiences ease after hardship:
(‘Ills have departed from me.) (Quran 11: 10)
Or in other words:
"Nothing evil or bad will befall me after this."
)'Surely, he is exultant, and boastful.) (Quran 11: 10)
('Except those who show patience and do righteous good deeds, those: theirs will be forgiveness and a great reward [Paradise].) (Quran 11: 11)