What is the scariest psychological disorder?

Part(i)

Capgras syndrome

Perhaps the most disconcerting mental disorder that exists, since those who suffer from it are sure that a close relative has been replaced by an identical impostor ...

The affected person has the firm conviction that a close person with whom there is a very broad bond, usually a relative with whom he lives, has been replaced by another person, an identical substitute. Most of the patient's questions are unanswered, which makes him live in a state of despair and causes strong feelings of fear and rejection of the person he considers an impostor.

Imagine this situation, you come back from university, open the door and meet a stranger, and the worst part is that this double looks a lot like a relative you love very much (your mother, father, brother ...) someone whom you know perfectly and with whom you share a home. But quietly you begin to notice that this person has some strange differences that make you think that he is not really who he seems ... he is someone else, probably a bad person. Where is your real father, mother, brother? How bad will the impostor's intentions be? It is not necessary to explain more to notice that this disease generates great psychological suffering to those who are afflicted with it.