True Happiness?

How can someone tell the difference between true happiness and deppression? Some poets say true happiness is the same as joy, but I think the difference is true happiness is feeling like that moment is truely the best you can feel without exploding. Is deppression really just feeling the same feeling with today, or is it like yesterday? Some people describe happiness as feeling light and angelic... but I don't believe that's true. True happiness or is it really being content......