What's the difference between bliss and happiness?
Bliss is a great deal stronger than happiness. You can be happy because it's not raining today, or because you found your glasses. But bliss is reserved for a state of complete, perfect happiness, such as what you may experience by finding your soulmate or having a transcendent spiritual experience.
Happiness is an emotion while bliss is a condition of the mind.
Emotions occur at an excited state of the mind and anything that's at an excited state comes back to ground state. Whereas bliss is a general state of the mind by itself, it doesn't take anything to do in order to attain bliss - it's just there. Whereas to feel happy, you need to do something like getting good marks, earning money, making friends,and so on.
The path to attain a state of bliss is through self contentment, where all your actions are done without ego involved - consequences don't matter but your willingness to do something is what matters.
About 3 years ago I checked into the ER with an obstructed bladder (due to kidney stones). The pain was unimaginable. Thankfully, the ER people recognized right away how much pain I was in and got me into a room right away. Several nurses got quickly to work, placing a "Foley catheter" in my urethra, draining the accumulated urine, and removing the pressure.
What I then felt was utter, total bliss -- a feeling of such incredible contentment and serenity that I cared not one whit that I was lying on a table with my pants down around my ankles and a tube hanging out. The sensation slowly diminished, but not for several hours.
I strongly suspect that true bliss cannot be achieved without some preceding hardship.