system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come when I'm stressed or worried my stomach becomes physically ill and gives me diarrhea?
gpt
When your stress levels are too high, you body goes into fight-or-flight mode. This is where you body redirects energy to the muscles so that you can fight something really well or run away from something really well.  
  
However, in stressful situations you might not actually be able to run away, but your body still redirects energy to the muscles. One of the places that no longer works receives much energy is your digestion system.  
  
Digestion takes a lot of energy to carry out, and we can make ourselves a lot stronger by using that energy to punch/sprint. When digestion stops, your stools will become either very hard or very soft. Diarrhoea is caused by digestion stopping, but fluids in your intestines still moving towards the bowel, which means you poop out a lot of fluids.