#9 Bray Wyatt, Dissociative Identity Disorder (DID)
Back in 1976, a TV movie called Sybil introduced the western world to Dissociative Identity Disorder, also sometimes called Multiple Personalities. While the patient portrayed in the movie had over 13 different personas, most patients with DID only manifest one or two extra personalities beyond their 'main' one.
It is easy to see how Bray Wyatt could suffer from this condition. His constant referrals to Sister Abigail as a separate person from himself are, in fact, quite in line with what DID sufferers experience in real life. In fact, oftentimes the different personas are unaware of each other. The alternate personas are sometimes of a differing gender or age than the patient's own.
Imagine Bray Wyatt trying to please a sister who exists only in his mind. It might explain why he seems so out of touch with societal perceptions of reality.
Treatment:
There is no known cure for DID, but long-term psychotherapy helps the individual deal with their symptoms. Since personality switches are often triggered by stress or anxiety, anti-depressants have been shown to be effective.
DID is extremely rare, so rare it is even considered to be iatrogenic, which means the patient's symptoms are brought on by the therapist's own suggestions. Bray Wyatt is not the type of man to trust modern medicine, so he may be a hopeless case.