system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What’s the science behind feeling your 'heart drop’ or getting a sinking feeling?

What does the body go through?
gpt
Typically, that sinking feeling is occurring in the digestive system. That sinking feeling usually occurs because of either something frightening or stressful occurred or you feel a sense of dread. This triggers your fight or flight response and your brain signals the endocrine system to release endorphins and adrenaline. Your muscles and body is now working on overdrive. The sinking feeling comes from your metabolism speeding up due to this release of chemicals. Food is now moving through your body faster then usual. What your feeling is your stomach being quick to hunger and rub together faster then normal and your intestines expanding and contracting faster then normal. This is the sinking feeling and in a way it’s aptly named since it’s caused by food sinking down through your digestive system faster then normal.