I always tested very high IQ, but only slightly better than average on acheivements. My father told me my whole life I was not living up to my potential, still does in little underhanded ways. Just be sure you do what you want to do. I was very good in math and science, but wound up in retail for the first 10 years of my work life after college. Many think I wasted my brain, but the truth is I had a lot of fun working in retail.
Worrying about what you should do when it is not really what you are inclined to do can be very paralyzing and anxiety provoking.
I will say this graduating from high school/college is one of the weirdest most stressful times in life. Did the severe anxiety start recently?
I spent about 8 years with free floating anxiety mostly related to a chronic illness. Here is what I learned which may or may not help you. Lack of control was a big contributor. I was at the mercy of doctors who were not listening to me. I was taking drugs and going through medical procedures that I many times did not agree with, trying to put my faith in the people who supposedly new better with few positive results. I felt sure I could be better, but I had many people telling me I should learn how to deal with my chronic pain and illness, accept it, but I was not willing to accept it, I endured it. Eventually I found a doctor who listened to me and I went through some treatment and got much better. The anxiety became much better. I also quit caffiene, reduced my work part-time, and began to really focus on the days I felt good.
I think if possible you need to learn or understand what is causing your anxiety, so you can try to undue the process. Maybe you are fearful of something? Maybe you mourn something? You have to be really honest with yourself, which at your age is difficult, because it is hard to know what you really want, to know yourself. This is where therapy might really help you. There are therapists who specialize in anxiety. There has been a lot of research recently on how avoidance creates severe anxiety, maybe that applies to you? Of course it could just be a chemical thing in the brain, but if you were not anxious until recently, I think this is somethig you can overcome. The brain is a complex organ. Right now it seems like your brain is in control, I have had that feeling myself, but over time, and with reframing events this can change.
Anxiety is paralyzing as I said above, I know. I would rather be depressed wanting to sleep all day in a dark room than have anxiety.
One last weird thing that I hae noticed, that probably everyone will think is strange. I have a muscle weakness problem, and when I tax my muscles a lot, by working out or just working in the yard for a few hours, the exhaustion seems to cause me anxiety. I have never read that anyone else has the same experience, but I only really narrowed this down because I had quit my job and was doing very little exercise of any sort. Then I began to realize when I do use my muscles I develop some anxiety, and then it subsides. Strange I know, but I just thought I would mention it.