Hey, I felt similarly when I was 25 as well. I passed 30 recently and am still here, and this video summarizes why:

https://www.youtube.com/watch?v=U88jj6PSD7w

What it boils down to is that the concept of happiness is just a cultural/social construct that doesn't necessarily need to be a priority in your subjective reality. Trying to adapt to exaggerated social norms for someone who doesn't experience fun easily can be toxic, and like Zizek, simply questioning the prevailing dogma that we all should live 'in the pursuit of happiness' can be a useful antidote.

Ask everyone you know what they think will make them happy. Much of the responses will be cookie-cutter shit -- something someone else thought. Doesn't it seem just a little strange that nobody can really quantify from experience what would give them lasting happiness and yet that abstraction is still what we're all expected to be chasing after?

If you're anything like me, focusing on your own path and finding meaningful work and hobbies can be life-saving. I don't worry about happiness because I have concrete goals to work on and seeing those goals to fruition is what I think really offers me tangible happiness, not chasing some pipe-dream that the collective unconscious has created for us.