Is the Fatihah the only part of the prayer that is not repeated if one doubts having recited it while in the following rak'ah? And does the prayer of one afflicted by obsessive doubts become invalid if they intentionally add a pillar, given that the addition is of the same kind as the prayer, such as repeating the Fatihah? And should the worshipper base their actions on the minimum if they have a medical problem with concentration and sometimes forget whether they bowed or not? And does this doubt dissipate by not paying attention to it?

If one doubts having omitted a pillar while in the prayer, it is as if they have omitted it. For example, if one doubts whether they recited Al-Fatihah or not, it is as if they did not recite it. This applies to those who are not afflicted by obsessive doubt (waswās). As for the one afflicted by waswās, they should not pay attention to the doubt; rather, they should assume they performed the pillar. For instance, if they doubt whether they recited Al-Fatihah, they should assume they recited it, or if they doubt whether they prostrated, they should assume they prostrated. If they do this and disregard the obsessive doubt, Allah will remove it from them.

Intentionally adding an extra physical pillar, like an extra prostration, invalidates the prayer. However, intentionally repeating the recitation of Al-Fatihah does not invalidate it, but it is disliked.