Severe depression, also known as major depressive disorder, is characterized by an intense and pervasive sense of despair, hopelessness, and anhedonia, or the inability to derive pleasure from most activities.

Individuals with severe depression may experience significant weight loss or gain, extreme sleep disturbances (either chronic insomnia or excessive sleeping), observable psychomotor agitation or retardation, debilitating fatigue, acute feelings of worthlessness or excessive guilt, marked impairment in concentration and decision-making, and recurrent thoughts of death, including persistent suicidal ideation or actual suicide attempts. 

The profound nature of these symptoms often disrupts daily life entirely and necessitates urgent professional care and intervention.