Which psychological condition involves persistent feelings of sadness and loss of interest?

The condition characterized by persistent feelings of sadness and a loss of interest is depression. This psychological disorder manifests through a range of emotional and physical symptoms, including prolonged periods of low mood, hopelessness, and a lack of interest or pleasure in almost all activities. Individuals may also experience changes in appetite, sleep disturbances, fatigue, and difficulty concentrating, which can greatly affect their daily life and ability to function.

In contrast, schizophrenia is primarily defined by a range of symptoms, including delusions, hallucinations, and impaired cognitive function, rather than a core focus on sadness. Bipolar disorder features cycles of mood changes, including episodes of depression and mania, making it distinct from unipolar depression. Anxiety disorders involve excessive worry and fear that can lead to avoidance behaviors, but they do not centralize around the pervasive sadness and lack of interest typical of depression. Consequently, depression stands out as the correct answer due to its defining characteristics of enduring sadness and diminished interest in activities.