After every happiness comes misery; they may be far apart or near. The more advanced the soul, the more quickly does one follow the other. What we want is neither happiness nor misery. Both make us forget our true nature; both are chains--one iron, one gold; behind both is the Atman, who knows neither happiness nor misery. These are states, and states must ever change; but the nature of the Atman is bliss, peace, unchanging. We have not to get it, we have it; only wash away the dross and see it.
The above makes a distinction between Bliss and Happiness. Happiness seems clear to fathom, but Bliss seems a bit fuzzy to define. I am unsure of the best way to do it.