RE: Absolute frustration!
I would sayif you find yourself locking up before you can get your pin lined up where you want it to be, do not release the arrow. I think if you release the arrow in this situation, then in your mind everytime you get into that situation where you get locked up, you will release the arrow as if it is aimed correctly and you problem will never be solved.
What i would do is if you can't move the sight and you are locked, just let the arrow back down and take a few breaths and redraw and try again. I had this problem when i first started out in archery and have corrected it by not shooting the arrow if you can't get your pins lined up where you want them.
Another thing you can maybe try at your house is to pull your bow back and aim at the target but do not shoot. Hold it back and move the sight all around the target WITHOUT shooting. Get the confidence that you can aim anywhere on the target before actually having to release any arrows to that location. That might help you get over the pin lock.