Is a brief sitting between the two prostrations to ensure tranquility considered an addition to the pillar that invalidates the prayer and necessitates its repetition?

It has become clear that the questioner is prone to obsessive thoughts, and has asked this question before.

His prayer was not invalidated; because a slight sitting does not invalidate the prayer, even if done intentionally, and a brief sitting, like the sitting for rest (jalsat al-istirahah), is excused.

Therefore, his prayer is valid, and he does not need to repeat it.