Emotional states that shift from high (manic) to low (depressive) characterize bipolar disorder. During the manic phase a person may be overly joyful and excited. During the depressive phase he may feel extremely tired and sad.
Mayo Clinic lists some factors that can trigger bipolar episodes. For example, bipolar disorder is common in people whose family have the condition, and stress can trigger episodes.
Bipolar disorder cannot be cured, but it can be managed through the use of mood-stabilizing drugs such as lithium.
A person can be affected by bipolar disorder at any time in her life, although the National Institute of Mental Health states that at least half of all cases begin before the age of 25.
According to Mayo Clinic, Bipolar disorder affects about 1 percent of the American population, although many cases go unreported.
Bipolar disorder causes intense shifts in mood, energy and activity level. If not treated, bipolar disorder can lead to severe depression, even suicide.