Exam anxiety is very common , and the reasons for it may be pressure from parents, our own expectations, any unhealthy previous experience during exams , comparisons with siblings and peers and sometimes due to exam phobia. You need to learn to relax before exams , do deep breathing exercise, study in chuks of 20 to 30 mins,relax for 10mins then restart studying, don't make long study plans like finishing whole course by a day or two, , plan for the next two hrs or so. But if you are having sleep problems, racing heart rate, difficulty in concentration, mood swings , then you may need professional help and mild anti anxiety meds.
All the best
Hi, you are tensed and facing anxiety because of two reasons. You show low self confidence and you also over do your preparations. You need to relax, take deep breathes and learn where to cut yourself some slack. You should speak with your parents and get a few counseling sessions just so that you would know how to handle the pressure and adopt better coping mechanisms.