What can a person do to maintain a feeling of contentment with themselves, while oscillating between a sense of happiness and comfort at times, and anxiety and fear of God's displeasure at other times?

True happiness and tranquility lie in obedience to Allah, while misery lies in disobeying Him. The true believer is one who is pleased by his good deeds and saddened by his bad deeds. The more a believer increases in obedience and closeness to Allah, the more at ease and tranquil he becomes. He must combine fear and hope, so he does not despair of Allah's mercy, but rather remembers Allah to remove distress and anxiety from himself, as Allah Almighty said: (Those who have believed and whose hearts are assured by the remembrance of Allah. Unquestionably, by the remembrance of Allah hearts are assured).