Your Body Prepares to Fight Danger
Your brain reacts to threats long before you consciously feel fear. It instantly floods your system with hormones to either fight or flee, turning your body into a survival machine.
This automatic response is designed to give you a massive burst of physical energy during an emergency. Your heart races and your senses sharpen to ensure you react fast enough to stay safe. Interestingly, modern life triggers this same survival mechanism for social stress, like speaking in public. It is a biological relic that saved our ancestors from predators but can feel quite overwhelming today.
Source: Fight-or-flight response