While not in the medical field, I reffed soccer for a decade and am quite familiar with the effects and treatment. Some guidelines:
Do not wait until you are thirsty. It takes at least half an hour after drinking fluids on an empty stomack for absorption to begin.
Have a regular drinking schedule - no joke.
Gatorade, while good, also must be consumed in advance.
Rule of thumb - if you are not urinating every other hour, you are not drinking enough. This goes for cold weather as well. Better a bit too much fluid than not enough.
If you are not sweating in weather like we had last Event, or notice anyone who is not and is flushed, immediately cease physical activity, drink a bottle, and take a 20 minute OOG break.
Do not be afraid to tell someone they are acting odd or need a break. I gave that advice and it turned out we had a wonderful time out while she rehydrated ( I sat with her, as did Clint). When a human NPC shambles and stumbles like a zombie, that's a good indication of dehyration (at night - during the day it could be heat prostration).
Edwin Haroldson
Loremaster
Master of the Mages' Guild
An ethical person does the right thing when no one is watching.
OOG - Charlie Spiegel - Kitchen Marshal
"War is a matter of vital importance to the State..."