The term "split personality" is outdated and not used in modern psychology. The correct term is "Dissociative Identity Disorder" (DID). People with DID experience the presence of multiple distinct identities or personality states within themselves, each with its own way of perceiving, relating to, and interacting with the world.
In the context of DID, it is common for the different personality states (also known as alters) to be unaware of each other or have limited awareness of the other alters' existence and actions. When one alter is in control, there might be amnesia or gaps in memory for what the other alters experienced or did.
However, it's important to clarify that people with DID are not "faking" or "pretending" to have these different identities. The condition is a complex and genuine response to severe trauma and is recognized as a dissociative disorder in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).
Although some alters may not be aware of the others, in some cases, co-consciousness can occur. Co-consciousness means that two or more alters are aware of each other's existence and may even communicate internally. This co-consciousness can vary in degree, with some systems having more awareness between alters than others.
Therapeutic approaches for DID focus on building internal communication and cooperation among the different identities to promote healing and functional integration. It's important to treat people with DID with empathy, understanding, and support, as they may face considerable challenges due to their complex condition.