Mental illness is a major theme in The Silver Linings Playbook. Pat and Tiffany both suffer from undiagnosed mental conditions, although in the movie version, Pat is described as having Bipolar disorder, and there are suggestions that Tiffany suffers from Borderline Personality disorder. In the book, Pat’s illness manifests as hallucinations (like his visions of Kenny G), outbursts of anger and violence, obsessive tendencies, and delusions (like his life being a movie produced by God). 

Tiffany describes her condition as no longer knowing “how to communicate with the people [she] love[s]” (284). She is also irrational, obsessive, and depressed. Tiffany’s guilt over Tom’s death exacerbates her symptoms. 

The football player Terrell Owens is also described as suffering from such extreme depression that he attempts suicide. He is also in therapy for his mental illness. Because he is a polarizing public figure, his condition is mocked by fans of opposing football teams. Pat’s condition is treated seriously and warily by his family members, but Owens’s struggles are fodder for sports gossip. 

One of the major hurdles that the other characters in the novel face as they deal with Pat and Tiffany is an inability to understand their perspectives. Their reactions are unpredictable because they are based on a logic that only makes sense to each of them, respectively.