How can one deal with despair over the continuous deterioration of one's psychological and physical condition, despite abundant supplication, seeking forgiveness, and charity, and the fear that this might be an affliction due to sins?

Calamities are expiations for sins, and patience through them brings reward and elevates one's status. Allah knows best what benefits His servant, and He is more merciful to him. He does not decree anything for His servant except that it contains a benefit for him. One should strive in supplication, patience, and contentment with Allah's decree, for: "No disaster strikes except by permission of Allah. And whoever believes in Allah - He will guide his heart." Have a good opinion of Allah and be optimistic, for indeed, with hardship [will be] ease. Rid yourself of obsessive thoughts and negative ideas, and be good to your husband and children.