I looked up mania in the dictionary and I didn't like what I saw. You can look it up too when you have the chance - it's right after madness and just before stupidity. Specifically, one dictionary I looked at referred to it as "A mood disorder; an affective disorder in which the victim tends to respond excessively and sometimes violently".
It is easy to read about bipolar disorder and learn how it is called the manic-depressive illness that levers you between phases of mania and depression at all kinds of indeterminate intervals. Sometimes you get the chance to function normally in between; sometimes you don't. However, I don't know if you have ever actually met someone in that condition before - someone who was actually being manic or depressive at a time when you were speaking with them. It is not a pleasant experience, I tell you. I'd like us to look at the mania for a moment.
Mania is obsession, and excessive and intense interest in someone or something, some kind of enthusiasm. But that is putting it mildly. Mania in the psychotic form is actually a psychiatric disorder characterized by excessive physical activity, rapidly changing ideas, and impulsive behavior. I'll help you understand: when you are manic, you are excited and enthusiastic, but you are never able to touch down on any one interest for any reasonable length of time.
Also, mania is an abnormal mental state that is characterized by an elevated irritable mood that is touched by self-importance, racing thoughts and hyperactivity. Did I mention a feeling of intoxication with you and with life? Or, are you manipulating people, spending money indiscriminately and pursuing sexual adventure to almost no end? And that is only the tip of the iceberg.