Getting slammed at the dojo

Dude. What a mind job! Acting is all about being honest, openly expressive of your deepest passions and energies so as to portray someone else and participate in a fiction. It's being truthful in order to most effectively be artificial. Similarly, ninjutsu is about being natural, open, responsive, relaxed, and not using strength, force, or tension in order to break someone who's trying to break you. HUH???
Hatsumi Sensei, and most of his students who've been my teachers, always tell us "Don't do a technique, don't fight the guy. If you do, you'll fail. Just be natural!" Meanwhile, this is in the context of these martial artists using the most subtle and complex maneuvers to break someone's balance and structure and to control them and beat the crap out of them. All without force and all without thinking about it.
HUH???
I've got pretty good technique, and I can apply it without thinking about it too much-on someone whose skills aren't as good as mine. That means I'm muscling it, at least somewhat. But I'm not aware that I'm doing that as I apply the techniques. All I know is that last night at the dojo, I got slammed. I couldn't break the structure or balance of the other black belt students.

(An aside: granted, I'm a new black belt, and black belts in ninjutsu don't mean you're an expert; "shodan", the first black belt grade, means "first level." It means you're a beginner, and everything leading up to black belt was elementary school. Now, I'm a beginning student, finally ready to learn.)

So, I was getting slammed. The teacher kept telling me to just respond naturally without thinking to a knife attack. By "naturally," he meant with the actual emotion of surprise and the adrenaline burst that comes with healthy fear. But relax and be responsive and flow unthinkingly with the situation. Well, a knife attack makes most people tense up! What the FRAK am I supposed to do? I have to be natural, but rewire my synapses somehow to be relaxed and natural under pressure and to do complex things without thinking, and not to use muscle when the fight-or-flight instict kicks in.
HUH???
I got a lot to learn....