Stupid Brain Stem Wants To Subdue That Chevy

Sometimes psychologists make a big deal about the "reptilian brain." They're referring to the brain stem, thought to be the earliest part of the brain to evolve, which controls very basic, unconscious processes (heart rate, breathing, etc.)--as contrasted with the limbic system, which is said to be the seat of emotions, and the neocortex, which enables us to reason. It's said that threatening situations trigger the reptilian brain's fight or flight instinct, which overrides rational processes. I've never found the supposed applications of this concept to everyday life to be very meaningful or helpful, with one exception.

The "fight" instinct always kicks in when I'm walking across the street and a car is approaching at a high speed. Although the calculations of my neocortex would indicate impact is very unlikely (it's rare that a motorist would intentionally mow down a pedestrian rather than stopping at a red light), an uncontrollable instinct takes over for a moment, and my body automatically stops in the middle of the road and braces itself for mortal combat with the oncoming vehicle. It only lasts for a moment, but it happens every time. No matter how many times the neocortex tries to inform the brain stem (for future reference) that "flight" would be a better option than "fight" in those cases, the stupid reptilian brain simply never learns.

Have other people experienced this? Do I have an overactive "fight" response, or what?