What is a defining symptom of a major depressive episode?

A defining symptom of a major depressive episode is persistent low mood. This symptom is a hallmark of major depressive disorder and reflects the pervasive sadness or emptiness that individuals often experience during this episode. The low mood can be present most of the day, nearly every day, and is often accompanied by feelings of hopelessness or worthlessness.

In addition to low mood, individuals may experience a range of other symptoms, such as changes in appetite, sleep disturbances, fatigue, difficulty concentrating, and loss of interest in previously enjoyed activities. However, the persistence of a low mood is central to diagnosing major depression.

Other options, such as increased energy levels, enhanced interest in activities, and excessive optimism, are contradictory to the typical experience of someone suffering from a major depressive episode and do not align with the core features of the disorder.