That's not what Camus is saying. It's not about literally feeling joy or sorrow. Happiness in this case refers to Sisyphus finding meaning and purpose in his suffering. Because suffering is all there is. You can find a reason to endure it, or you can kill yourself. Those are the only options. Some people don't realize that because they're fools who have never observed the reality they live in, but that doesn't change the bare facts of the matter.

All life is is choosing what you want to do with the time between now and the moment you die.