There are several types of depression, which can be grouped into endogenous (medical or biological) and exogenous (situational).
Major and persistent depressive disorders are commonly exogenous in that they are borne of external events such as traumatic or stressful circumstances. This might be diagnosed if symptoms have been consistently experienced for more than 2 weeks, persistent being symptoms for more than 2 years.
Depression brought on by chemical or hormonal imbalances are commonly bipolar disorder, psychotic depression, seasonal affective disorder, post-natal depression and premenstrual dysphoric disorder.
Atypical depression is slightly different than the persistent sadness of major depression. It is periodic in nature with periods of remittance where external events control moods.
The severity of depression is mainly determined by the impact symptoms have on daily life. A mild episode has some impact, which is perhaps not even noticed by others. Moderate depression has a significant impact on daily life which is likely to be more obvious to perhaps family members or work colleagues. Severe depression has a debilitating impact on everyday life.
