This feeling is called disassociation. Disassociation is described as being detached from one's self and believed to be a type of coping mechanism. Additionally, psychologists associate disassociation to a trauma experienced by a person in their childhood. It is believed that if a mind of a person could no longer handle stress, it finds a way to disconnect from reality. However, disassociation has a shorter duration than psychosis, where there is a complete loss of contact with reality.
