system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does drinking fluids help when you're sick?
gpt
Truth of the matter is no one knows for sure but we have some ideas, it might be all of these, or none at all.

First of all the obvious, if you're sick enough you're losing water by sweating feverishly, having diarrhea and throwing up, then you're keeping yourself from being dehydrated and dehydration can make you feel pretty miserable.

Second, being dehydrated makes you feel crappy, so of you're lightly dehydrated plus sick then you're feeling double-crappy.  Supporters of this theory point to comfort food and the desire to engage in soothing activities like warm baths when sick.

Third, most of the feeling crappy when you're sick is actually the result of your body's own immune response, causing inflammation, fever and other responses to fight infection.  A minor cause is the remains of destroyed cells and if it's a bacterial infection, bacterial toxins.  Being well-hydrated helps your body eliminate these toxic substances more easily.  We're not sure about immune chemicals but excess might be excreted by the kidneys.

Another theory says when you're sick your metabolism is increased and you need more water to help things along.

Truth of the matter is it's not certain which factors play into it, but it's probably a complex combination of factors.