Well, unhappy IS the converse... it's a snapshot of a time that was very bad.

Not being happy doesn't equate to unhappiness. Maybe in writing sure, but not in real life. Happiness isn't two state of beings, it's a spectrum. Often, in our day to day lives, we reside near the middle of the spectrum, neither overtly happy or not, just content. Some moments of our life shift us closer to either end, but to constantly live in a state of pure joy is to live in a utopia - and we all know how that ends.

The above is a healthy person, a person whose neutral state rests near the middle of the spectrum. A depressed person would be one whose neutral state rests near the "unhappy" side of the spectrum. It is unhealthy for a person to be giddy 100% of the time; in the same sense, it is unhealthy for a person to always be miserable.

In the end, to decipher your own happiness and whether or not you should change, you must first clear your mind of any one person's definition of happiness. Forget everything you've learned or been taught because it's all pressures of a society made by humans for humans. Look into yourself and determine: Am I content? What do I want to change? Is it reasonable to want these things to change? Is so, how will I change them?