Happiness is an Economic Issue

Happy People Perform Better
Why is the UN investigating happiness? Why do some countries have a Minister for Happiness? And why is there even a country that judges national legislation based on Gross National Happiness?
There must be a good reason for this. Happiness determines whether people are healthy and productive. Not only does it feel good, but it is also of economic importance.
What can you do to be happy, or at least not unhappy?