Yikes! If you fail the exams, it, unfortunately, doesn't matter how well you do with everything else.
Obviously, if you're doing well with the material in class and at home, there's not really a problem with your absorption and understanding of it. It seems like it really is your fear of exams is causing you this problem.
I would also recommend that you talk this over with your professors, but, in addition, your school probably has some counselling and/or mental health services that you should take advantage of. If anyone can help you with your test anxiety, they can.
Most importantly, though - GET HELP ASAP! Exams count for such a huge portion of your final grade that you won't want to go too long getting bad results on them before you just fail out of college altogether.