There are several different types of medically recognized depression. The most common type of depression is called major depression, and it occurs when your symptoms interfere with your enjoyment of life or daily functions — including your work, sleep, and eating habits — for at least two weeks straight.

Some people experience only one episode of major depression in their life, while others may go through numerous episodes of the illness.

In comparison, people with another condition known as persistent depressive disorder — also known as dysthymia — experience less severe mood symptoms that last continuously for at least two years.

During this time, there may also be periods when the person experiences major depression.

Other common types of depression include:

Postpartum depression, in which mothers experience symptoms of major depression after giving birth (mood impairment is much stronger, and lasts longer, than the “baby blues” that many new mothers experience)
Seasonal affective disorder (SAD), in which depression sets in during winter (and sometimes fall) and is associated with a lack of sunlight.

Psychotic depression, in which severe depression is paired with some form of psychosis, such as delusions and hallucinations
Premenstrual dysphoric disorder, in which symptoms of depression develop a week before a woman’s period and pass after menstruation.

Some people who experience depression may have bipolar disorder — formerly called manic-depression illness — which is characterized by moods that cycle between extreme highs (mania) and lows (depression).