What does forgetting the middle rakʿah in prayer necessitate?

If someone forgets a pillar, such as bowing (rukuʿ) or prostration (sujud), they should return to it as long as they have not reached its position in the following rakaʿah (unit of prayer). If they have reached its position or passed it in the following rakaʿah, they should complete their prayer and then perform an additional rakaʿah to replace the one in which the pillar was forgotten, and then perform the prostrations of forgetfulness (sujud al-sahw). However, if someone forgets an entire rakaʿah, the rakaʿah they are currently performing serves as a replacement for the forgotten one, and they should then complete their prayer. If someone forgets the first tashahhud (middle sitting) and their hands and knees have left the ground, they should complete their prayer and perform the prostrations of forgetfulness before the salām. But if their limbs have not left the ground, they should return to the sitting position and complete their prayer, and there is no prostration of forgetfulness required of them.