We've all experienced mood swings, so it's easy to think bipolar disorder is just a fancy name for one.
When most people feel in the dumps or on top of the world, it's usually a short-term feeling that fades away along with the reasons that prompted the feeling, or as a result of a gradual adjustment to the new circumstances.
Bipolar mood swings are different, and they can last for weeks or months. Up mood swings often lead to dangerous lifestyle choices, racing thoughts that refuse to be corralled and out-of-ordinary behaviors that can damage careers and family lives. Down mood swings for a bipolar person lead to excessive sleep and lethargy, uncontrollable crying and even thoughts of (and attempts at) suicide.
So when we're talking about bipolar disorder, we're not talking about good moods and bad moods. There's no "snapping out of it" when it comes this condition.