Bipolar depression is part of bipolar disorder. It refers to the "low" parts of the disorder.
Symptoms of Bipolar Depression
Thoughts of death or suicide
Loss of energy
Difficulty sleeping - sleeping too much or not sleeping at all
Changes in appetite - eating too little or too much
Difficulty concentrating or performing basic activities
Loss of interest in things you once enjoyed
Bipolar I
In order to be diagnosed with bipolar I, you must have had at least one manic episode and one depressive episode (manic episodes may sometimes result in hospitalizzation). Manic episodes include: -excessive energy -restlessness -difficulty concentrating -feelings of euphoria -risky behavior
Bipolar II
In order to be diagnosed with bipolar II, you must have major depressive episode lasting 2 or more weeks and a hypomanic episode. People with bipolar II don't usually have manic episodes bad enough to lead to hospitalization. Bipolar II can often times be misdiagnosed as depression because it mainly displays signs of depression. Hypomanic episodes are like manic episodes, but not nearly as bad. There are never any psychotic features durning a hypomanic episode and they do not interfere with work or socializing.