Your sympathetic nervous system floods you with adrenaline and cortisol. Heart rate climbs, breathing turns shallow and high in the chest, peripheral vision narrows, and blood is shunted away from your prefrontal cortex, the part of you that nuances, negotiates, and chooses words carefully.
In a business context this is why you go blank in a Q&A, snap at a teammate, agree to something you didn't want to, or replay a 30-second exchange for three days. It isn't a character flaw, it's physiology overriding strategy.