Does the prayer of one who is excessively doubtful become invalid if he prostrates for forgetfulness after he thought he had completed his prostration, and then doubted?

A person who experiences frequent doubts should ignore them and not perform the prostration of forgetfulness (Sajdat al-Sahw), so as not to add to the prayer while being certain of its completion. There is no need for her to repeat the prayer, and her prayer is valid.