In simple terms, the polar opposite of depression is called MANIA. It involves symptoms like excessive happiness, irritable mood, excess talking, grand and elaborate plans, believing oneself to be powerful, belief of having special abilities, loss of sleep and appetite, increased energy.
Usually, Mania occurs in episodes along with episodes of depression in between. This is called Bipolar disorder.
What essentially happens is a person shifts between feeling extremely happy and extremely sad over a period of months or years. Each episode can last for months.
Being a chronic and serious illness which can significantly disable the patient, it requires medication.
Mood stabiliser therapy combined with anti-depressant or anti-manic drugs can help control the symptoms and in many cases lead to long term remission.