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What is Endogenous depression and explain in detail?
Endogenous depression (melancholia) is an atypical sub-class of major depressive disorder (clinical depression). It could be caused by genetic and biological factors. Endogenous depression occurs due to the presence of an internal (cognitive, biological) stressor instead of an external (social, environmental) stressor. Endogenous depression includes patients with treatment-resistant, non-psychotic, major depressive disorder, characterized by abnormal behavior of the endogenous opioid system but not the monoaminergic system. Symptoms vary in severity, type, and frequency and can be attributed to cognitive, social, biological, or environmental factors that result in persistent feelings of sadness and distress. Since symptoms are due to a biological phenomenon, prevalence rates tend to be higher in older adults. Due to this fact, biological-focused treatment plans are often used in therapy to ensure the best prognosis.Endogenous depression was part of the Kraepelinian dichotomy system.

Signs and symptoms
The forefront indication that a depressive episode is manifesting is the sudden loss of energy or motivation in daily routines. When this occurs, it is not uncommon for individuals to seek medical attention with excessive worrying or anxiety that a more severe, physiological disease may be the underlying issue. However, without an actual disease present, this neurotic thinking often results in severe anxiety, sleep disturbance, and mood swings which may hinder social relationships. Individuals with endogenous depression may experience inconsistencies in symptom severity  which is often the reason for delayed treatment. If left untreated, symptoms may progress to a major depressive episode.

Risk factors
Endogenous depression occurs as the results of an internal stressor—commonly cognitive or biological—and not an external factor. Potential risk factors include these cognitive or biological factors. Patients with endogenous depression often are more likely to have a positive family history of disorders and fewer psychosocial and environmental factors that cause their symptoms. A family history of depression and perceived poor intimate relationships are internal risk factors associated with this type of depression