Malbim: A Tzadik's body can perish, and Hashem is blameless, for afflictions of the body are not real afflictions. Loss of the body is not a loss, for man is primarily the Nefesh, which is clothed in the body. Afflictions purify it to return to its place and receive its reward in the eternal world, which is the primary place of reward and punishment. "Atah Amal Tishkach" - the primary you, i.e. the Nefesh. When you will remove the garment of physicality from you, you will forget the body's toil and afflictions.

Rashi: So there will be no memory of sin.

Devar Eliyahu: There are three kinds of sick people. (a) His body is blemished. (b) His strength is weak. (c) Due to much worry in the heart. "V'Hesir Hashem Mimecha Kol Choli" is thought (worry), which is worse than all of them. "Ki Az Tisa Panecha mi'Mum" exempts from the first. "V'Hayisa Mutzak" saves from the second. "Ki Atah Amal Tishkach" - your heart will not worry. He will forget all his afflictions, and not feel them, even if his mouth mentions them, like water that passed and there is no trace of it.

Malbim: You will remember the body's toil and afflictions like water that passed and flooded the ground. At the time of the flood it was a terrible evil, but the coming year, they remember it for the good. The water made the ground fat and moist. Chazal said, one blesses on the bad that is like good. If his field was flooded, now it is bad, but it is good for the future - it will deposit mud (it makes the land more fertile). So afflictions in this world are beneficial for the life of the Neshamos.