Bipolar disorder is characterized by episodes of mania, or hypomania, and depression. Mania is an overly "high" period. Hypomania is a milder form of mania. Depression is a "low" period.

People with bipolar I disorder have alternating episodes of mania and depression. Individuals with bipolar II disorder have alternating episodes of hypomania and depression. Four or more episodes of mood swings in a 12-month period is known as rapid-cycling bipolar disorder.

What is going on in the body?

Bipolar disorder is a disorder of the brain. Researchers believe that chemicals called neurotransmitters are involved. Nerve impulses cause the release of neurotransmitters from one nerve cell to the next. This release allows cells to communicate with one another. Too little or too much of these important neurotransmitters may be released. This can cause or contribute to bipolar disorder. Some of the neurotransmitters believed to be linked to bipolar disorder are serotonin, norepinephrine, and dopamine.

What are the causes and risks of the condition?

Usually bipolar disorder first appears when the person is between the ages of 15 and 25. Teens who have had a major depressive episode are at greater risk for developing bipolar disorder in their late teens or 20s.

While the exact cause of bipolar disorder is unknown, genetics does seem to play a role. Fifty percent of all individuals with bipolar disorder have at least one parent who has a mood disorder.