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.
test anxiety happens to me; i get nervous and realize later that i would of done better if i had relaxed a bit :)
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.