i've had more first hand experiences of dehydration/heat exhaustion than i'd like to admit. ppl say it's good to sweat, it cools the body when one is working out. that's only true if one is able to concurrently replenish the fluid loss. for most ppl, that's not a big problem cos they don't sweat too much but when i sweat, i get drenched. by my estimation, i lose at least 3 times as much fluids thru sweating than the average person within the same time period, doing the same physical activities, under the same environmental conditions. you know you're dehydrated when you start seeing bright spots but the most extreme case of dehydration i'd experienced left me blind for at least 5 min, i couldn't see with my eyes fully open. that shit is scary. prolonged dehydration can lead to permanent damage at the cellular level. it is no joke. if you feel it coming, get help immediately. it's no time to play it cool, or act tough. ask a stranger to run to the nearest 7-11, 3 blocks away, and get you a 1.5L bottle of H-two-O, if that's what it takes. cos you won't make it there in time yourself....now on a lighter note, check out what dehydration did to me 10 years ago ( 1:38 onwards )