Well, it seems you are experiencing anxiety associated with test taking which is normal, you just experience it more than usual.
In my opinion, it may work if you see a cognitive therapist who can help you go through techniques of self hypnosis, which is more of a relaxing technique. My therapist said that it works great if you know you are gonna take a test and can be quick when you get good at it.
I'm practicing myself at it (i'm not very good) but I do feel more relaxed when I try it.
Thats just my suggestion.
test anxiety happens to me; i get nervous and realize later that i would of done better if i had relaxed a bit :)
Gotta learn to take the consequences out of the test and just see it as a fun game and as your time to have your say rather than just having to listen to the teacher. I know tests do have consequences, but what doesn't? It's more like playing chess than it is education, so treat it as such. Might help demystify the whole thing for you.