Many people refer to feeling sad or disappointed as “being depressed”. This is a factually incorrect description. Depression is, in part, a chronic change in one’s mood, outlook, or behavior. Normal sadness and disappointment don’t linger on for weeks at a time.
Bipolar Disorder is a swing between feeling euphoric mania, and major depression. Bipolar Disorder can have a severe impact on the lives of people inflicted with it, as the euphoric mania stage sometimes results in excessive, irresponsible behavior — spending a great deal of money unwisely, for instance, or inappropriately interjecting oneself into certain situations — while the major depressive stage can leave a person almost completely incapacitated, and sometimes leads to a suicide attempt.
Having anxiety is quite a different scenario than having Bipolar Disorder. Anxiety is, generally speaking, feeling emotionally overwhelmed and/or extremely fearful, be it most of the time, or only in certain situations. The person with anxiety may feel as though they aren’t in control, but an anxious person typically isn’t going to engage in public displays of irrational or unreasonable behavior like someone with Bipolar Disorder may. Interestingly enough, this fear of becoming mentally ill is typically an indication that one is not mentally ill at all, as most people who are truly mentally ill consider themselves to be normal and healthy, and may even react hostilely to anyone suggesting otherwise.
While using the term mood disorder when one really means anxiety may just be a case of semantics, it is important to differentiate between various emotional and psychological conditions, if for no other reason than to ensure proper treatment.