The exact cause of Multiple Personality Disorder is not clear, but it's often linked to severe trauma during early childhood.

Serena Williams explains her various personalities—and reveals she's given each one a name. “Summer is my assistant who lives inside my body,” Williams said. “It's weird. She's very effective.

Schizophrenia is a chronic, severe mental disorder that impacts the way a person thinks, acts, expresses emotions and perceives their reality. It is not a common disease and is prevalent in less ...