I don't know, but I've known people like this. One woman turned out to be lying completely, even though she did seem grounded. She became completely hysterical when I met my husband, telling me lies about him, and him lies about me and my son, in an effort to split us up. Turned out that my husband knew her history... that she'd never had an American boyfriend who died in a motorcycle accident, that she'd never been pregnant and lost her babies, etc etc.

Sometimes even seemingly "grounded" people can be living in a fantasy world.