I'm not sure I even know what happiness is, at least in the sense that NT people use the word. I guess the closest I've ever come to understanding that was when my daughter was born.
Otherwise, I've known contentment for brief periods, but I don't know if that's the same thing. Maybe it is, I'm just not sure I understand "happiness" as a concept. I know Boredom, Loneliness, Depression, Anxiety, Anguish, Panic and Despair all too well, for me "happiness' is just the absence of any of those.
Strangely, I have had dreams on rare occasions in which I experienced intense, transcendent levels of positive emotion that I have never experienced in real life. Elation, joy, ecstasy, inner peace - states I had only read about before. How wonderful to die in one's sleep during a moment like that and remain forever in that alternate universe. 