When you are dehydrated, you are using more water than you are taking in. This can be caused by fever, vomiting, diarrhea, or simply not drinking enough water. Symptoms include weakness, dizziness, and fainting. If you are dehydrated, drink more water or sports drinks and cool down your body temperature. Sometimes medical care is needed, especially if you have a high fever. Follow the links below to find WebMD's comprehensive coverage about how dehydration is caused, its symptoms, how to treat it, and more.