Assalamu alaykum, when you are praying and you recite sura al-fatihah, then you has started to recite an ayah, but then you think you has not recitetd the previous ayah correctly and therefore you return to the previous ayah and you recite it again. Have you thereby added something to the prayer which is not a part of it and so you have to do sujood as-sahw? Are those prayers valid where you haven't done sujood as-sahw (although you could imagine that you have to do it, but you were not sure)? Jazakum Allahu khayran.

All perfect praise be to Allaah, The Lord of the Worlds.  I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

If a person doubts whether or not he has recited a verse of Chapter Al-Faatihah, then he is obliged to recite it again and his prayer does not become void by him doing so. An-Nawawi said in Al-Majmoo’: “Also, if one doubts that he has not properly recite a verse of it [Al-Faatihah], he is obliged to recite it again in a correct manner.”

Nevertheless, we advise you to put an end to your whispers as you have asked about 40 questions and most of them are about whispers. So, you should fear Allaah and close the door of whispers as it seems that you are deeply affected by them. Indeed, you should avoid these whispers so that you can perform your acts of worship in a proper manner because opening the door of whispers leads to a great evil that will be very difficult to get rid of.

Therefore, if you have whispers about the recitation of Al-Faatihah, then you should recite it once only and not take into consideration the whispers of the devil that you might not have recited it in a correct way or that you might have made a mistake in reciting one letter and so on. The treatment for whispers is to neglect them and avoid them and there is no other treatment for them than this.

Allaah Knows best.