James 5:13

Verse 13 Is any among you afflicted? let him pray.

In the place of denying the faith under oath, let such a one pray pray for strength to bear the affliction and every persecution. God alone is the helper in all times of trial.

Is any merry? let him sing psalms.

I think the word "cheerful" or "joyous" gives a better and a more proper view. Any such is enjoined to show his joy in singing praise to God for his mercies. Prayer is the best means of producing within us patience and resignation under all oppresive circumstances, and singing the praises of God in psalms is the proper way of showing our cheerfulness rather than in ribald jest or lewd song.