system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why when I'm hungover do I not seem to want water/food even though I need it and will make me feel better?
gpt
To specifically address the lack of appetite, it's usually inflammation-related.  Alcohol irritates the lining of the stomach and intestine.  The brain takes those sensory signals and says "something's not right in the GI tract, let's not put anything else in there until we're sure everything is ok".

Alcohol also affects the balance system in your inner ear as well, which can contribute to nausea depending on your tolerance for a lack of equilibrium.

In the end, there are lots of factors that contribute; alcohol is a very small molecule and can go pretty much anywhere in the body, causing different effects in different places.  Very ELI5 but hopefully that answers your question!