system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Survival experts will tell you to not chug water or stuff your face with food after being found dehydrated and malnourished. Why?
gpt
Refeeding Syndrome has been covered for food, but what about water?

When you are dehydrated, Anti Diuretic Hormone is released, causing your body to retain sodium ions. Your blood sodium rises and slowly equilibrates with your brain sodium level. If you drink a lot of water quickly, blood sodium drops quickly but brain sodium stays high. This creates osmotic force that pulls water into the brain, increasing pressure to dangerous levels. This results in cerebral edema, seizures, brain damage, or death. 

TLDR; quickly rehydrating a dehydrated person could pop their brain.