you know how a person can daydream about being somewhere else. example when my wife and I plan a family trip sometimes I will run through our plans in my mind, daydream how it may be....well some people with some mental disorders have an internal world thats kind of like that only it has a sense of reality to it.

Example I know someone with schizophrenia. their internal world is a fictional planet, only to them it is a real place that they escape to.

another person I know with DID, their internal world is a room where all their alters come together to talk, play,do things together.

Another person I know that has DID their internal world is barbies dream house. when they dissociate they are mentally living a life in barbies dream while the alter is in control of the body and taking care of things outside the body (work, school what ever needs to be done)

a persons internal world can be anything that they need to survive, a place in their mind they go to while the alters are in control of the body.