Hi, I can help with the information on split personalities! I am currently an honors psychology student, and I will be studying to be a criminal profiler/psychologist in the near future! Here is some information below!-
Dissociative identity disorder (commonly known as multiple personality disorder) is the presence of two or most distinct personality states. These other personalities may all have a unique name, personal history, ages, and characteristics (Ex: personalities name is john, and while your character may have grew up in the bustling city of new york in 2019, this personality John may be from a rural farm in Kentucky in the year 1875). The disorder is a reaction to trauma that can help the brain avoid bad memories. The trauma tends to happen in childhood, and as a way to cope, the child dissociates and splits into parts. One part usually endures the emotional or physical impacts, and the other exists afterwards. So a personality might be scared by something that reminds them of that past trauma. The personalities are NOT always aware of each other, though they can be.
This disorder is something that requires a medical diagnosis. Behavioral wise, the person may experience impulsivity, self-destructive behavior, or self-harm. Mood wise, the person may experience anxiety, detached from self, or mood swings. Psychologically speaking, the individual may experience altered consciousness (a temporary change in one’s normal mental state without being considered unconscious. This includes having hallucinations, hypnotic states, trance states, and meditation), depression, or flashback. Other common symptoms are amnesia or blackouts.
There is little form of treatment. The treatment consists mostly of talk therapy (going and seeing a psychologist). There is also cognitive behavioral therapy, family therapy, and psychotherapy that can be used. The lack of therapy is due to the fact that DID often goes unrecognized in the scientific community. Scientists and psychologists will doubt it’s existence, and it often gets diagnosed as schizophrenia.
That is a lot and there is definitely so much more information out there, but that’s the ‘basics’. If you have any questions about this or other things relating to DID, feel free to ask!