system
Given the following post, respond as if you're commenting on Reddit:
human
What is happening, physiologically, when we get those uncomfortable butterflies in our stomach that are frequently associated with public speaking, getting in trouble, or seeing an ex in a new relationship?

Lately, whenever I get particularly nervous or stressed about a romantic situation, I get a churning acidic feeling in my stomach that prevents me from eating and being productive. I've both experienced and heard this experienced frequently as well with examples from the title, and I'm just wondering what's going on.

Is there an actual change to our body chemistry when we're stressed or emotionally hurting that causes this? Would there be any way (without removing the emotional stress) to counter this?
gpt
Being in a stressful or even a nervous situation cause your digestive system to become inhibited; relaxing your stomach muscle and changing it chemical composition.

It does this because for most of human history stress typically involved a fight-or-flight situation that required our muscles.  Temporary shutting down the digestive system frees more blood for the muscles, and causes the release of glucose (sugar) to your muscles.  It may not be a life-or-death situation but remember your body was adapted for the plains of Africa, not the hall of high school.

You may also notice that in uncomfortable situations your breathing and heart rates increase.  There is a nervous system that connects your brains to most of your organs called the sympathetic nervous system.  The sympathetic nervous system regulates your body in a "fight-or-flight" situation.  There is a second nervous system, called the parasympathetic nervous system, that keeps your body in a "rest-and-digest" state.  Thus everytime you see your ex with her new boyfriend your parasympathetic nervous system is turning off and your sympathetic nervous system is ramping up.