Persistent low mood, loss of interest, and a sense that ordinary effort is pointless mark major depression. Sleep, appetite, concentration, and self-worth usually suffer as well.

Depression can arise after loss or chronic stress, yet it also appears without obvious external cause. Biological factors—genetics, neurotransmitter systems, inflammation—interact with cognitive styles such as rumination and negative self-evaluation. Episodes range from mild to severe and can be recurrent.

Evidence-based treatments include antidepressant medication, cognitive-behavioral therapy, interpersonal therapy, and, for severe cases, neuromodulation techniques. Behavioral activation—re-engaging with rewarding activities—often helps even when motivation is low. Social support and reduction of stressors improve prognosis. Depression is treatable; untreated, it raises risk for further episodes and for physical health problems.

The illness convinces the person that recovery is impossible, which is itself a symptom that treatment must address.