Major depression, defined as a single bout or recurring episodes of depression, is the most common form of depressive disorder; however, there are several other types of depression. Persistent depressive disorder, or dysthymia, or a less severe but longer-lasting form of chronic depression. Manic-depressive illness, or bipolar disorder, is characterized by cycles of extreme highs and lows. Seasonal affective disorder, or SAD, is experienced when sunlight exposure is decreased. Postpartum depression is the change in mood and behavior of a woman as a result of the hormonal changes, lack of sleep, and lifestyle changes that follow childbirth. Psychotic depression is when major depression or manic-depressive illness is experienced along with delusions
