Is the saying "If you are afflicted by sins, conceal yourselves" a Prophetic Hadith or a saying of the Companions, and is affliction from Allah or due to human actions, and what is the relationship between this and the Western saying that calls for seeking treatment or not grieving?

The saying "For every disease there is a cure" is Islamically sound. If someone is overcome by their desires and falls into sin, they should conceal themselves and not expose their sin, as stated in the Hadith: "Whoever commits any of these abominations should conceal himself with Allah's concealment."

As for trials and tribulations, they are from Allah, who tests His servants with good and evil, to distinguish the obedient from the disobedient. Allah Almighty said: "And We test you with evil and with good as a trial." Allah has shown mankind the path of good and evil so that they may choose what they wish. If one errs and falls into sin, they should conceal themselves.

The Western saying agrees with Islam in not grieving over what has passed, but Islam emphasizes that for every disease there is a cure, and for every problem there is a solution, as stated in the Hadith: "Be keen on what benefits you, seek help from Allah, and do not be helpless. If anything befalls you, do not say, 'If only I had done such and such, it would have been such and such,' but rather say, 'Allah has decreed, and what He wills, He does.'"