Is someone who utters a word of shirk to himself—without uttering it aloud—considered a mushrik due to waswas, and is there a behavioral treatment that can be prescribed for a chronic obsessive-compulsive disorder, especially with the fear of falling into shirk, and the presence of other waswas related to progeny, prayer, and ablution?

Obsessive whispering (waswasah) is one of the most dangerous ailments. One must struggle against oneself to turn away from it and not pay attention to it, because it is a trick of Satan to divert from worship and distance from good. All the obsessive whispers that arise, all the prayers for harm that are uttered against children, all the polytheistic thoughts that cross one's mind, or that are uttered involuntarily, none of this harms or affects the soundness of faith. One must turn away from these whispers and repel them until Allah grants healing. For behavioral therapy, you can consult the counseling section on the website.