Is it obligatory to repeat a fard prayer that was performed while sitting due to fatigue, if the fatigue subsides before the prayer's time expires?

Standing in obligatory prayer is a pillar without which the prayer is not valid, provided one is able to do so. However, one who is unable to stand may pray while sitting. The difficulty that permits sitting in prayer is that which removes khushu' (devotion), presence of heart, and tranquility. So, if standing becomes extremely difficult, to the extent that it disturbs the worshipper and prevents them from finding peace, then it is permissible for them to sit. If one prays sitting due to an excuse, and then their excuse disappears after completing the prayer, they are not required to repeat it.