Lycanthropy

 Let me introduce you a lycanthropy disorder. In this case patients believe that they are not human beings but animals. Therefore, they exhibit the behaviours characteristic for a given animal. Patients are the most often convinced that they have turned into a wolf, although sometimes they think that they are other animals, including a dog, a frog, a cat, a horse, a tiger, or even a boa snake.

Lycanthropy is a very rare type of delusion, but when it occurs, all symptoms are very specific. They include belief that you are the animal, inability to look critically at this type of delusion and a lack of rational reflection. Patients try to present evidence of their animality. They imitate animals, useing typical for them movements, as well as sounds and noises, for example they howl like a wolf. They manifest fangs and claws.

Lycanthropy is very often a symptom of schizophrenia, bipolar disorder or severe depression. According to doctors an important factor contributing lycanthropy may be a damage of the brain part, which is responsible for perceiving one's own body. 

The treatment plan for lycanthropy disorder is always determined individually, depending on the diagnosis. The basis of treatment is pharmacotherapy. In most of cases doctors recommend antipsychotic drugs, which eliminate hallucinations and delusions. Psychotherapeutic treatment can be started later, after symptoms have been calmed down. It helps to understand the mechanisms of the disorder and regain control over one's own mind.

https://www.livescience.com/44875-werewolves-in-psychiatry.html

https://the-gist.org/2015/08/clinical-lycanthropy-where-psychiatry-and-mythology-collide/