system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does your heart get that sinking feeling when something bad happens?
gpt
Fight or flight response gets activated. Your body shuts down digestive system. Your body also opens up blood vessels near the heart to send blood to your muscles while shutting down bloodflow to non survival areas like the skin and intestines. Your heart also starts to beat faster and harder to make sure it's moving blood at peak power.  You also start breathing heavier to get more oxygen into the bloodstream.