Is an affliction that impairs one's religion (such as distraction in prayer or reduction in good deeds) a good or a bad affliction? And is its cause a sin, or what? And is contentment required in it?

Everything that befalls a believer by way of tribulation is good for him, because if prosperity befalls him, he is grateful, and if adversity befalls him, he is patient. Allah records for him the reward of the deeds he used to perform before the tribulation. The tribulation may be due to sins and transgressions. Contentment with Allah's decree is recommended but not obligatory, and it does not contradict taking lawful means to remove the tribulation.