Fight or Flight is (too often IMO) used as an excuse (for improper training). When examined in the wild (with animals), it doesn't (really) occur (as described). It is always dependent upon different factors, and (of course) which creature is the predator, and which is the prey.
It was this same premiss that Taika would "poo-poo" regarding the Chinese systems that were based around animal's ("human's aren't animals, they don't have claw's, or fang's, but they have far greater intelligence,... they just don't use it", LOL).
Understanding what is emotionally as well as physically occurring during this initial segment of an assault, allows the student to modify their training to compensate for any deficiency's that may occur or be present at that time. The greatest factor (to any corrections that need to be made), is that by being aware of them, they can be corrected and/or eliminated, as the student requires.