I had really bad anxiety problems. Started out like you're saying here, I think it was all to do with my life at the time, things were stressful and nothing was going well (e.g. parents divorcing, mum being suicidal, sudden deaths of quite a few close family members and friends, etc etc.) And on top of that, I was doing 5 AS levels at college, all fairly hard subjects, and was hating college anyway without really knowing why. I had everything I could need there, escapism, a social life, lots of friends. Half way through the year, for no apparent reason, I just stopped going. I preferred to stay at home and lie on my living room floor for hours at a time, in front of the fire, just thinking, staring into space. After a year, I started having panic attacks, really bad ones where I thought I was going (and sometimes wanted) to die.
It took until I was 20 to get myself back into shape. I got a drinking problem, I got a gambling addiction, I ruined my long-term relationship with my boyfriend and I temporarily moved out of home. It was an awful period of my life that I regret, as I'm sure it will hinder me now (like you, I had good GCSEs and was immediately snapped up as a potential Oxbridge candidate in my first year at college).
What I would do if I could turn back time...
1. Go to a doctor, sort out some counselling, you can get it for free if you're on the NHS (I'm not sure about private health care?) And just get talking, talk yourself through everything.
2. Put a few hours aside, and figure out for yourself what would make you happy. Do you think you could see yourself getting through this year at college? If not, it might be best to act fast to avoid getting yourself a bad reputation as a student (and preventing you from maxing your potential in the future). Just keep perspective, you're a clever person - maybe studying could help you?
3. No matter how hard it is (because I know it's VERY hard), try not to worry about yourself. Worry about others, worry about the world, worry about anything you want, but don't over-analyse yourself. Don't diagnose yourself with the worst potential depression that's possible. Tell yourself that you're stressed and that you need breathing time, some time for yourself.
4. If you decide to carry on with your education (which I think could be best, though it's not for me to decide), remember to make time for you. Even if it makes you feel silly, do something really relaxing and calming. Go for a walk.
I'm back in education now, and I still feel things piling on top of me sometimes. I had three books to read and two essays to write in two evenings last week, and all you have to do is keep sight on your goals and ambitions and do it optimistically. I put time aside for myself, at least once or twice a week, where I can really *chill*. Sometimes this means sitting in my bed, writing, reading or even just thinking. Other times I go for a walk, I write poetry by the lake near to my house, or I go for a jog.
I think you're potentially your own worst enemy right now. And as long as you are always looking after yourself, your future, and your own happiness, you're one million miles stronger than I was.