At least, that's the message I received from the wrapper on my Dove's Dark Chocolate Promises candy.
Is happiness contagious? I don't know, really. I suppose that happiness could be contagious, sometimes. But my general impression is that isn't necessarily so. The Declaration of Independence* asserts that all individuals possess the right of the pursuit of happiness, but makes no statement whatsoever regarding the actual state of being happy. I'm guessing the question of attaining happiness made even the founding fathers a little bit uncomfortable.
*Of course, one's judgement on whether or not the Declaration of Independence serves as any sort of authoritative document, whether philosophically or otherwise, is entirely subjective.