Does the prayer of a person afflicted with obsessive-compulsive disorder become invalid if he repeats a letter or a pillar, and when is prostration of forgetfulness (sujood al-sahw) obligatory upon him?

The person afflicted with whisperings (waswas) should not pay attention to his recurring daily doubts, and he is not required to perform the prostration of forgetfulness (sujud al-sahw). If he repeats a letter or a pillar of the prayer, his prayer is not invalidated, and he is not required to perform the prostration of forgetfulness.