Dysthymia: Dysthymia is a milder but longer-lasting form of chronic depression. It involves experiencing depressive symptoms for at least two years but not as severe as major depressive disorder.
Double Depression: Double depression occurs when an individual with dysthymia experiences a major depressive episode on top of their existing chronic low-grade depressive symptoms.
Persistent Depressive Disorder (PDD): PDD is another term used to describe chronic depression or dysthymia. It refers to long-term depressed mood that persists for at least two years with intermittent periods of less severe symptoms.