Depression, also known as depressive disorder, is characterized by significant and persistent depression and is the main type of mood disorder. The depressed mood can range from sullenness to grief, low self-esteem and depression, or even pessimism and anxiety, and may include suicide attempts or behaviors; some cases have significant anxiety and motor agitation; severe cases may have hallucinations, delusions and other psychotic symptoms. Each episode lasts at least 2 weeks, or even several years, and most cases have a tendency to have recurrent episodes, most episodes can be remitted, some may have residual symptoms or become chronic.