What defines major depressive syndrome?

Major depressive syndrome is defined by a depressed mood lasting at least two weeks along with a variety of symptoms that can significantly impact a person's daily life. These symptoms may include changes in appetite, sleep disturbances, feelings of worthlessness or guilt, difficulty concentrating, fatigue, and even thoughts of death or suicide. The key characteristic is the persistence of mood disturbance over an extended period, indicating that it goes beyond situational sadness and qualifies as a clinical condition that requires attention and treatment.

In contrast, the other options describe conditions or states that do not capture the essence of major depressive syndrome. Feelings of happiness for extended periods, a lack of interest in physical activities only, or consistent energy and enthusiasm do not relate to the defining features of depression, which focuses on prolonged sadness and the broad array of symptoms accompanying it.