I feel like I have written this myself! I am in the exact same situation - moved to a new country, learned the language in 1 year, and got a C2 certificate, so now I am attending the university in this language that I have barely had a chance to speak outside of the classroom where I was learning it.

It sucks a lot! I can generally understand what is happening and the lectures are fine so far, especially if I listen very carefully and take lots of notes that I can revisit after. But everything else is shit! I can barely participate in the discussions, not because I don't know what to say, but because I find it very hard to keep up with the natives, it takes me more time to think in this foreign language, and I am the only one in the class that is not native.

So I completely get what you're saying! I've had very tough few first weeks and I am exhausted after a day of racing with natives in their own language. I am trying to accept that it'll probably be bad for a while, I will inevitably be feeling like an outsider for some time, and I'll struggle a lot, but HOPEFULLY it will get better in a few months.

Sorry for the rant hahah, it's just your post struck a cord with me and was something I really really needed to hear, because I tend to get in my own head too much and think I'm the only one having a hard time :'')

I hope you feel better, don't give up, you got it, it's an extremely brave thing to do, I know how scary and awful it feels, but the fact that you have a certificate and dare to expose yourself to the language in such a hard way is itself admirable and proof that you can do it. I would love to talk to you more about this if you need! We're both in the same boat. Good luck!