Can you give examples of how your body reacts to stage fright?
if I'm nervous my hands tend to get cold and tingle. Then my hands start to freeze and become hard to move, especially whenever I'm playing on the piano.
Can you record a video of yourself playing for someone to check if you're maneuvering your hands in a painful way? E.g., when your body gets stage fright, you might unintentionally bend your wrists up or down which might interfere with your tendons and blood vessels -- restricting blood flow or twinging nerves.
Even if the idea of recording a (small) performance makes your body stressed, remind yourself that you want to observe any physical oddities so that you can improve them.
Also, do you practice vocalizing your performance? I don't mean sing it, but rather get the pitches roughly correct but with good timing. I find that by vocalizing a piece first, you're teaching your brain how to perform it, which helps teach your body how to perform it as well.
