What is the ruling on excessive involuntary swaying while standing in prayer, and is the imamate of one who does so valid?

Swaying during prayer is considered disliked (makrooh), based on the Hadith (definition): "When one of you stands for prayer, let him tranquilize his limbs and not sway like the Jews." What is disliked does not invalidate the prayer unless it becomes frequent and continuous. If the swaying becomes so excessive that it invalidates the prayer, then the prayer of the one performing it is invalid, and consequently, his imamate (leading of prayer) is not valid.