Just as the manic aspect of bipolar disorder is associated with manic episodes, the depressive aspect of bipolar disorder is likewise associated with depressive episodes. The severe form of depressive episode is known as a Major Depressive Episode.
Someone having a Major depressive episode must experience five or more of the following symptoms during the same two-week period for most of the day or nearly every day:
- Feelings of sadness, emptiness, or hopelessness (in children, this may be irritability)
- Having no interest or feeling no pleasure in all or almost all activities
- Weight loss or weight gain by greater than 5% when not trying to lose or gain weight OR a change in appetite nearly every day
- Sleeping too little or too much
- Physical agitation or restlessness that is observed by others
- Being tired and having a lack of energy
- Feelings of worthlessness, self-hate, and guilt
- Not being able to concentrate, think clearly, or make decisions
- Being irritable
- Ongoing thoughts of death or suicide - either thinking about suicide without a plan for how it would happen, having a specific plan or attempting to commit suicide
Depressive symptoms can vary a great deal from one person to the next. One person with depression may experience feelings of sadness, hopelessness, and helplessness. Another person may feel angry, irritated, and discouraged. These symptoms may also seem like a change in someone's personality. For example, someone who is usually patient might begin to lose his or her temper about things that normally would not bother him or her.
Symptoms can also change over time when someone is depressed. Someone who is initially withdrawn and sad can become very frustrated and irritable as a result of getting less sleep and not being able to accomplish simple tasks or make decisions. These symptoms cause stress that is noticed by others and cause problems at school, work or in relationships with others.
Unlike with mania and hypomania, there is no short-term depressive episode that can be diagnosed. There is a related condition known as Persistent Depressive Disorder, or Dysthymia,, which describes a long-lasting mild depression. Dysthymia cannot be diagnosed at the same time as bipolar disorder. This is because in order to qualify for a diagnosis of Dysthymia, you have to show evidence of consistently mild depressive symptoms occurring more days than not over a period of at least two years. The presence of manic or hypomanic episodes during the two-year period would disqualify a person from being diagnosed with Dysthymia.
While bipolar disorder most frequently happens as a swing between manic and depressive episodes, in a minority of cases, a third type of episode can happen. One of the specifiers for Bipolar Disorder can be "with mixed features." This means that the criteria for mania and the criteria for depression are both simultaneously met. However, just because criteria for both manic and depressive episodes are both met during a single day, for example, does not mean that both sets of symptoms are present at the same time. Instead, what typically happens is that there is a rapid switching between manic and depressive states, happening one or more times in a single day. These mixed features tend to be severe when they occur with psychotic symptoms such as hallucinations and delusions, and suicidal thinking frequently present.