Mental breakdown (also known as a nervous breakdown) is a non-medical term used to describe an acute, time-limited phase of a specific disorder that manifests primarily with features of depression or anxiety.

The terms "nervous breakdown" and "mental breakdown" have not been formally defined through a diagnostic system such as the DSM-IV or ICD-10, and are nearly absent from current scientific literature regarding mental illness. Although "nervous breakdown" does not necessarily have a rigorous or static definition, surveys of laypersons suggest that the term refers to a specific acute time-limited reactive disorder, involving symptoms such as anxiety or depression, usually precipitated by external stressors.

Specific cases are sometimes described as a "breakdown" only after a person becomes unable to function in day-to-day life.

Causes of such breakdowns are varied. A 1996 study found that problems with intimate relationships, such as divorce or marital separation, contributed to 24% of nervous breakdowns. Problems at work and school accounted for 17% of cases, and financial problems for 11%. Surveys suggest that in the United States, health problems have decreased in importance as a contributor to nervous breakdowns, as these accounted for 28% of nervous breakdowns in 1957, 12% in 1976, and only 5.6% in 1996. Though in themselves, nervous breakdowns are considered a "health problem" by most professionals.

James Douglas Muir "Jay" Leno /ˈlɛnoʊ/ (born April 28, 1950) is an American stand-up comedian and television host.

From 1992 to 2009, Leno was the host of NBC's The Tonight Show with Jay Leno. Beginning in September 2009, Leno started a primetime talk show, titled The Jay Leno Show, which aired weeknights at 10:00 p.m. (Eastern Time, UTC-5), also on NBC. After The Jay Leno Show was canceled in January 2010 amid a host controversy, Leno returned to host The Tonight Show with Jay Leno on March 1, 2010.

James "Jay" Leno was born in New Rochelle, New York, in 1950. His mother, Catherine (née Muir; 1911–1993), a homemaker, was born in Greenock, Scotland, and came to the United States at age 11. Leno's father, Angelo (1910–1994), who worked as an insurance salesman, was born in New York to immigrants from Flumeri, Italy. Leno grew up in Andover, Massachusetts, and although his high school guidance counselor recommended that he drop out of school, he later obtained a Bachelor's degree in speech therapy from Emerson College, where he started a comedy club in 1973. Leno's siblings include his late older brother, Patrick, who was a Vietnam veteran and a lawyer.