Is the feeling that acts of worship (prayer, remembrance of God, reading the Qur'an) are burdensome during bad psychological states, in contrast to how it feels during good states, considered a weakness of faith, or is the strength of faith variable?

The madhhab of Ahl al-Sunnah wa al-Jama’ah holds that faith increases with obedience and decreases with disobedience. The feeling of constriction during worship may be due to committing transgressions, and it is remedied by repentance, remembrance of Allah (dhikr), and contemplation of death. For the sweetness of faith, Allah and His Messenger must be more beloved to a person than anything else, and one must love another only for the sake of Allah, and detest returning to disbelief. Likewise, one who is pleased with Allah as their Lord, with Islam as their religion, and with Muhammad as their Messenger tastes the flavor of faith.