Bipolar disorder, also known as manic depression, is a mental illness that brings severe high and low moods and changes in sleep, energy, thinking, and behavior. People who have bipolar disorder can have periods where they feel overly happy and energized and other periods of feeling very sad, hopeless, and sluggish. In between those periods, they usually feel normal. You can think of the highs and the lows as two "poles" of mood, which is why it's called "bipolar" disorder. The word "manic" describes when someone with bipolar disorder feels overly excited and confident. These feelings can also involve irritability and impulsive or reckless decision-making. About half of people during mania can also have delusions (believing things that aren't true and can't be talked out of) or hallucinations (seeing or hearing things that aren't there). "Hypomania" describes milder symptoms of mania, in which someone does not have delusions or hallucinations, and their high symptoms do not interfere with their everyday life. The word "depressive" describes when a person feels very sad or depressed. Those symptoms are the same as those described in major depressive disorder or "clinical depression," a condition in which someone never has manic or hypomanic episodes. Most people with bipolar disorder spend more time with depressive symptoms than manic or hypomanic symptoms.