in a new environment he is a spaz who can't deal with the adrenaline dump.
I think this is the most important thing to note. If you practice a certain situation very often, your body stops dumping adrenaline at that situation, it is used to it. When you change the situation, even slightly, your body might decide it is adrenaline time once again, and you will have to face the adrenaline flow all anew.
I doubt there is any real solution to this type of problems. You could practice full contact sparring in a competition every other day, but a surprise attack would remain something new to you, create an adrenaline dump and place you at that place once again.
We should strive top learn how to ride the wave, and flow with it, since the adrenaline dump is a biological phenomena we, as people, only have limited control over. It seems to me the adrenaline dump and overcoming it, were part of the attraction the Samurai found in spiritual practice and meditation - as a way of improving byond the mere physical aspect. Not sure if it is true, does it work and can we duplicate it today.