Major depression is one of the most common mental disorders in the United States. For some individuals, major depression can result in severe impairments that interfere with or limit one’s ability to carry out major life activities.

• Major Depressive Disorder is a period of at least two weeks when a person experiences a depressed mood or loss of interest or pleasure in daily activities, and has a majority of specified symptoms, such as problems with sleep, eating, energy, concentration, or self-worth.

–NIH

Persistent depressive disorder (also called dysthymia) is a type of depression in which the individual has a depressed mood that lasts for at least two years. A person diagnosed with persistent depressive disorder may have episodes of major depression along with periods of less severe symptoms, but symptoms must last for two years to be considered persistent depressive disorder. Those with dysthymia usual experience mild symptoms of depression that are not debilitating or impact their ability to function.

–NIMH

Postpartum depression is much more serious than the “baby blues” (relatively mild depressive and anxiety symptoms that typically clear within two weeks after delivery) that many women experience after giving birth. Women with postpartum depression experience full-blown major depression during pregnancy or after delivery lasting longer than 2 weeks. The feelings of extreme sadness, anxiety, and exhaustion that accompany postpartum depression may make it difficult for these new mothers to complete daily care activities for themselves and/or for their babies.

–NIMH

Bipolar depression is very common in very common in Bipolar I and Bipolar II disorders. It is characterized by episodes of extremely low moods that meet the criteria for major depression mixed with extremely high – euphoric or irritable – moods called “mania” or a less severe form called “hypomania.”

–NIMH

Seasonal affective disorder is characterized by the onset of depression during the winter months, when there is less natural sunlight. This depression generally lifts during spring and summer. Winter depression, typically accompanied by social withdrawal, increased sleep, and weight gain, predictably returns every year in seasonal affective disorder.

–NIMH