How to continue prayer if one found out he missed or added a rak'a or a part of the rak'a?

Question

My point is what exactly should a person do in the moment he/she realize that he/she missed or added a part of rak'a to his prayer.
Here two exemplary situations:

• I stood up after finishing the 4th rak'a (and maybe missed the tashahud) and while reciting Quran realized that I'm in my 5th rak'a should I immediately sit and do the tashahud and the sujud a-sahw or complete the rak'a I began?
• I missed the 2nd of the two sajdas and stood up and realized I have missed the sitting between the sajdas and the 2nd sajda should I immediately transfer to the sitting between the sajdas and complete from this point, or complete my prayer from the "position" I was at actually?

I'm looking for a practical answer: What is more correct going back to the point where the mistake has been done or continuing and performing sujud a-sahw?

Answer 1

All Praise to Allah Subhanahu wa Taala and blessings of Him be on Prophet Muhammad peace be upon him His family and companions

The answers below are according to Sunni Hanafi view,

Sajdah Sahw (Forgetfulness prostration) is wajib when one or more wajib acts of the prayer are missed.

--For your first situation If you stood up after finishing the fourth Rakah and have not performed the sajdah of this Rakah then immediately sit down before the Sajdah and do Sajda Sahw,however if you have performed the sajdah for the fifth rakah then this prayer would be counted as Nafl Paryer and you have to redo for your fardh or wajib prayer.

--For your second situation if you missed one of the sajdah then perform the missed sajdah at the same time and continue your prayers as you have to continue after this sajdah and in the end do sajdah sahw for this prayer.

Allah Swt and His Messenger knows best.