What is the reason for a person to feel chest tightness and a lack of trust in God and in the answer to prayer, despite their increasing knowledge and understanding of religion, and their diligence in acts of obedience and avoidance of sins?

Constriction in the chest and a lack of spiritual expansion for supplication (du'a), along with weak trust in Allah, could be from the machinations of Satan, or due to a forgotten sin, for sins bequeath alienation between a servant and his Lord. Therefore, one must renew repentance from all sins, and increase in seeking forgiveness (istighfar), remembrance (dhikr), and reading the Qur'an, for by the remembrance of Allah do hearts find tranquility. It is not a condition to recall the sin for the validity of repentance. It is also recommended to seek the prayers of one's parents, for the supplication of a parent for their child is answered.