It is possible that you are suffering from a form of anxiety and/or depression which might respond to treatment through discussion with a doctor or other appropriate clinician.
Although I enjoyed my time at Oxford and liked my subject, between Christmas and Easter in my final year I experienced real stress for the first time in my life. I felt pinioned by the weight of work I had to do for my exams. I spent almost every weekend of that Hilary Term hunkered down at at home (my parents were very kind to me at that time). I saw my college doctor, and I also took up running. By the beginning of Trinity Term, I had regained focus and energy, and I got to work and did well in my exams.
Suggestions: talk to your friends, your family, your tutors and/or your college's pastoral staff about your feelings. These people will usually want to help you. Socialise. Finalists should not lock themselves in their rooms working non stop. They should take breaks, meet up with friends for a meal, go to a movie etc.
Obviously, be careful not to use alcohol or recreational drugs (if you happen to be partial to either, ignore this if you are teetotal) as props. Do not self-diagnose, and do not self-medicate!
If friends etc who are not clinicians offer diagnoses, politely disregard them. They mean well, but they are not qualified to diagnose you. Even your medical student friends are not yet doctors. If having a drink or getting a little buzzed makes you feel happy, then do so in careful moderation. When the fun stops, stop. I repeat: do not self-medicate!
Try to increase your exercise levels - even going for a walk can help. Use whatever method of exercise works for you, be it running, swimming, gym, rowing, pilates, squash, yoga, whatever. The mind and the body are a dualism (Descartes was wrong). Eat healthily and don't skip meals. Try to enjoy the good things in life - food, conversation, books etc.
Maybe talk to a doctor for a clinical view of whether you are depressed and might benefit from a course of anti-depressants, but bear in mind that these can take several weeks to start working. The most commonly used types are what are called Seratonin Re-uptake Inhibitors. They adjust how much seratonin is active in your body during a day
If Oxford is bugging you, consider spending some time at home, or otherwise away from the city.
Don't worry about loving or hating the law as a subject. Just treat the exams as a technical task to be completed. The minute you walk out of the Examination Schools after your last exam, you can forget everything you ever knew about the subject, throw your gown in a skip, and, if you like, leave Oxford and never go back (or see how you feel in thirty years time). You are not under any obligation to collect your degree in person if you don't want to. I know people who have still not graduated despite passing their Oxford exams decades ago.
Employers in many sectors don't much care about what you studied at university. If you can get a 2.1, great. Even if you get a 2.2, it's not the end of the World. Maybe in future years, when the grey clouds have long since passed away, you will make light of it, and feel able to assert bragging rights for having a Desmond.
Remember: in the future, what is now the present is the past. Nothing lasts forever. The only direction of travel is forwards.
Good luck. I hope that your can find a path to being happier.