system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can a conversation have an effect on you that can cause you to break in to a sweat, get very dizzy, sick to your stomach and almost make you pass out?
gpt
You have a nerve that communicates with your stomach (and many other organs)--the Vagus nerve. It is in the back of the neck, but from there, it attaches to every major organ--vagus means "wanderer" in Latin. (Edited spelling) 

When you experience emotion, like in an intense conversation, that nerve communicates with stomach, diaphragm, and other organs and you can feel that "nervous" feeling in your stomach or butterflies in your belly. 

Once you feel it, you can grow anxious about the feeling (What's wrong with me?) and get more anxious. That creates the experience you talked about, where you almost pass out. 

Or, you can respond to the feeling your brain is giving you and try and find a situation (either through a change of situation or a change of your mind/thoughts about it) where you have less stress and anxiety. Then you'll feel better and not get that sick feeling.