So, I had a university interview the other day. It went monumentally, historically, tremendously badly. Every time I was asked a question that I was perfectly capable of answering, and would've been able to answer if just given it on a piece of paper and locked in a room alone, my general thoughts were along the lines of "**** **** **** **** I NEED TO COME UP WITH AN ANSWER SOON OTHERWISE I'LL LOOK LIKE AN IDIOT AND GET REJECTED", rapidly followed by "**** **** **** I NEED TO STOP THINKING "**** **** **** **** I NEED TO COME UP WITH AN ANSWER SOON OTHERWISE I'LL LOOK LIKE AN IDIOT AND GET REJECTED" SOON OTHERWISE I'LL GET REJECTED", ad infinitum, until I was put out of my misery. Which, was rather frustrating, given that I'd put a lot of preparation into this, and I'd rather undeservedly come across as a complete moron. Firstly, I seem quite unable to let this go, even though clearly there's not a lot I can do about it now, and am just sitting around moping and feeling sorry for myself, and so I'd rather like some advice on how to just get over it.
Secondly, I have an interview at Oxford in a week and a bit. Now, in the intermediate time, I'm feeling a bit ****ty, because I'm pretty sure preparation will be futile because of how little it's helped elsewhere, but, of course, when I do anything other than prepare, I just get more and more nervous, and can't see the point in it - but when I try and prepare, I just start thinking "This is so ****ing pointless, this isn't going to help", and so don't get anywhere with that. And, of course, I'm also just consumed by a general feeling of dread, because I get the feeling that, whatever happens, the same panic that overcame me before will just resurface, and as such my confidence in my ability is at an all time low, which doesn't really help, because that just gets into a cycle of gradually getting a worse and worse outlook on things.
tl; dr: I'm a ****, I panic a lot, then obsess too much about how badly I panic/ how badly I'm going to panic. How do I calm myself down/ get a bit of confidence back?