Depression is not a single, unified disorder, and it affects people differently. The depressive disorders encompass a wide spectrum of moods and emotions -- from persistent sadness, apathy, and anxious agitation, to crippling negativity and despair.  Depression can flare up in episodic bursts, cycle rapidly through mood states, and consume entire weeks, months, even years with its punishing bleakness. Sometimes it is embedded in, or masked by, medical illness. Often it manifests as physical pain.

Depression is variously described as a mood disorder, a brain imbalance, a mental state, a physical disease, emotional dysregulation, personality disorder, or disturbed cognition.  Classification systems, such as the Diagnostic and Statistical Manual of Mental Disorders (DSM), reduce depression to a set of observable symptoms, which, while descriptive, is an oversimplification.  A more comprehensive explanation is that depression is a psychobiological disorder - a product of interacting genetic, psychological, and environmental factors. But no clinical definition truly captures the devastating impact of depression, an anguish that casts its grim shadow over every aspect of life -- self, memory, sleep, endurance, ambition, appetite, will, competence, intimacy, desire.