system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does it feel better to curl up in a ball when you have a stomach bug?

Every time I get a stomach bug, pain, or other ache in my stomach, I just curl up in a ball and it gets better, but why?
gpt
It seems that lying in the fetal position (curled up in a ball) has some sort of deeply comforting physical and psychological effect on people. Many people who have gone through severe trauma will go into this position. Most people also sleep in some variant of this position - lying on their side with their knees tucked up and body curled forward. People also tend to be comforted by having a thick blanket put on them. For this reason emergency workers have such blankets on hand for victims of trauma. Even some animals respond to this - blankets are used in rehabilitating orphaned elephants to provide psychological comfort. So one reason that curling up makes you feel better could be psychological comfort. 

The other thing is that curling up reduces the tension on your abdominal area. If you lay out all straight or stand up, your abdomen is being pulled taught and increasing the pressure/stimulation to your GI tract. As you probably have experienced even something usually insignificant like a waistband or seatbelt can worsen nausea. So a position that decreases stimulation in that region would help you feel better.