drastic physiological changes happen with the activation of what's called the fight-or-flight response of the sympathetic nervous system. The zebra's heart rate increases, the breathing increases, large amounts of stress hormones like cortisol and adrenaline are released into the bloodstream, pupils dilate, the blood pressure increases, and any non-essential functions like digestion stop.
— Matty Stratton · Fight, Flight, or Freeze - Releasing Organizational Trauma, London 2019 · at 2:12