Natalie Vincent (Kelly Rowan) is, Daniel's best friend and every bit his intellectual equal. Natalie is Daniel's most reoccuring hallucination. She appears mostly in circumstances where Daniel is either alone, or in need of some guidance. She usually offers advice that Daniel disdains or mocks, usually in retort to what the right thing to do is. When Daniel tries to solve a problem, her input usually cuts through the bullshit, and tells him what he denies. Throughout the show she is portrayed as maybe a lost loved one to Daniel, kept alive in his mind for the sake of love, and she may be the subliminal cause to his delusions. But she respects Daniel, and obviously loves him as much as a hallucination could. Out of all his hallucinations, when caught talking to them, by Max or Kate, he is never flustered or ashamed when it's Natalie.
In the Season 1 Finale, it is revealed that Natalie is actually a hallucination that Daniel created in his junior year of college and is actually based on Doctor Caroline Newsome who he saw at a party at Michigan when they were students.