First aid for dehydration?
Also, if your feel your heart is beating fast or irregularly you need to go to an ER because your electrolytes are off. If you've had diarrhea and/or vomitting for more than 48 hours, go to the doctor or ER if you're really bad off and can't wait. It's not something to play around with. Drink Pedialyte or Gatorade if you can keep it down and keep cool...even if you feel cold.
drink sports drinks to restore electrolyte balance (e.g. gatorade)
suck on ice chips
if the person has a temperature/ has been exposed to heat
remove excess clothing
put in shade/air conditioning
spray room temp water with mister (dont use ice water or ice packs)
take to hospital if it is bad, people have died from severe dehyrdation
Drink fresh water and try to remove yourself from sources that will make you perspire unnecessarily. Additionally, try to avoid dry foods, as digestion requires water.
Some information: http://www.webmd.com/search/search_results/default.aspx?query=dehydration&sourceType=undefined