system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does it suddenly feel like our hearts drop everytime we see or do something startling like a teacher calling us over to their desk?

Admit it, you got scared whenever a teacher called you over.
gpt
The release of adrenaline (more accurately called Epinephrine) is a hormone released by your adrenal glands, preparing you for a fight or flight scenario. 

The release of adrenaline speeds up the beating of our hearts and it's that fluttering sensation that makes it feel like our 'heart is dropping', when something scary or nerve racking is happening. 

EDIT: Grammar.