Rashi on TanakhPsalms 41

the poor Heb. דל, the ill, to visit him, as the matter that is stated (in II Sam. 13:4): “Why are you so poor (דל)...?” mentioned in reference to Amnon.

on a day of calamity This is Gehinnom (Ned. 40a). And in this world, what is his [the visitor’s] reward?...

The Lord will preserve him and keep him alive i.e., the visitor and benefactor who visits him and benefits him.

on his sickbed Heb. ערש, lit in French, as (in Deut. 3:11): “Behold his bed is an iron bed.” When he too takes ill, He will support him. What is the meaning of “on his sickbed”? This is the seventh day of the sickness, when he is very ill. In this manner, it is explained in Aggadath Tehillim (Mid. Ps. 41:5).

when You have transformed his entire restfulness in his illness Even in the time that his illness has become more acute, when all his restfulness and tranquility have been transformed.

I said, “O Lord, be gracious to me” As for me, I have none who visit for good, and when I cry out from my illness and say, “O Lord, be gracious to me, etc,” my enemies rejoice over me and say evil things about me: “When will he die, etc.”

he speaks falsely He pretends to be troubled, and when he sits before me, his heart gathers thoughts of violence to himself, [of] what evil he will speak when he leaves, and when he goes outside, he speaks of it.

whisper about me something that is harmful to me, and what is that thought?...

An evil thing shall be poured into him All the wicked things that he did shall be poured and spilled into his body, and if he lay down, he shall not rise. This is how they curse me.

developed an ambush for me Heb. עקב, an ambush, as (in Josh. 8:13): “and their ambush party (עקבו) on the west of the city.”

With this I shall know, etc. When You are gracious to me and raise me up, I shall know that You have desired me; when my enemy will not shout with shouts of joy over me, and I will see that because of my innocence, You have supported me.

Blessed is the Lord When I stand up from my illness, I will bless You in this manner.