What is the syndrome where actors think that they are the character they act as?

The syndrome where actors believe they are the characters they portray is often referred to as "role immersion" or "method acting." While method acting is a legitimate technique used to deeply connect with a character, some actors may experience a more extreme form where they struggle to separate their identity from that of the character, potentially leading to psychological issues. This phenomenon can lead to challenges in personal relationships and mental health, as the boundaries between their real lives and the roles they play become blurred.