system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: when you are sick with a stomach bug why is actually Happening inside you that makes it so uncomfortable?

Headaches, gas, muscle soreness, vomiting and diarrhea are all things that you feel when you are sick with a stomach ‘bug” why does it actually hurt so much? And what is happening internally as it goes thru your body?
gpt
Your immune system is fighting an invasion of microbes that have snuck into your body through food.  The vomiting and diarrhea is your body's way of forcing out the contaminated food as quickly as possible.  The body and joint aches come from your bone marrow producing more white blood cells to fight the bacteria before it becomes a life or death situation when bacteria enters the bloodstream and fever is your body's way of playing chicken with the bacteria by turning up the heat so much that it damages the bacteria but it has to be careful not to go too much as that will cause brain damage.