• Major Depressive Disorder (MDD): Commonly referred to as clinical depression, MDD is characterized by persistent feelings of sadness, hopelessness, and a lack of interest or pleasure in activities. Other symptoms may include changes in appetite and sleep patterns, fatigue, difficulty concentrating, and thoughts of death or suicide.
• Persistent Depressive Disorder (Dysthymia): This is a chronic form of depression that lasts for at least two years. People with dysthymia may experience milder symptoms than those with major depressive disorder, but the symptoms persist over an extended period.
• Seasonal Affective Disorder (SAD): SAD is a type of depression that occurs seasonally, typically during the fall and winter months when there is less sunlight. It is thought to be related to changes in light exposure.

• Bipolar I Disorder: Characterized by episodes of mania (elevated mood, increased energy, impulsivity) and depressive episodes. Manic episodes can be severe and may require hospitalization.
• Bipolar II Disorder: Involves periods of depression and hypomania (a less severe form of mania). Individuals with bipolar II may not experience full-blown mania but still have significant mood swings.

A milder form of bipolar disorder characterized by chronic mood disturbances involving hypomanic and depressive symptoms. The symptoms are less severe than those in bipolar I or II.

These categories encompass mood disorders that do not fit neatly into the other classifications but still involve significant disruptions in mood.