The medical world classes depression as belonging to dysfunctional psychological illness (others include panic, anxiety, dread, compulsion etc.). It is a type of physical and mental illness, in which physical, emotional and mental states are affected.
醫學界將憂鬱症歸屬於精神官能症的一種（其他包括恐慌症、焦慮症、畏懼症、強迫症等），是一種身心性的疾病，包括生理、情緒及思想都會出現特殊症狀。