Dehydration is when the body fluid levels drop. This can be because of loss of fluids by sweating or because too little fluids were consumed. Dehydration can become an issue with long term bondage and fetishware that covers a large portion of the body with materials that do not allow the skin to breath.
Mild dehydration is usually starts with thirst and a dry mouth. Moderate dehydration also includes dizzyness and eventually fainting.
All but the most severe cases of dehyration are easily treatable at home. Lay down in a cool place with your feet proped up. If the body was covered with latex or similar materials, wipe off the sweat with a cool moist towel. Then drink lots of fluids. Water, juices and sports drinks work best. If you experience dizzyness for longer than an hour, you should seek professional help.