Does the noble verse, "And whoever He wills to send astray, He makes his breast tight and constricted," apply to me, given the setbacks I experience in worship, and feelings of tightness, doubt, and hardness of heart? Is there a way back to a spacious breast and certainty?

The aforementioned verse is about disbelievers, and the questioner should ward off doubts and whispers and not surrender to them. He should strive to compensate for the acts of obedience he has missed, have a good opinion of Allah, seek His help, exert effort in supplication, accompany the righteous, adhere to remembrance [of Allah], and acquire beneficial Islamic knowledge.