All About Dehydration
Tired? Having difficulty concentrating? You might be dehydrated without knowing it

When you lose more fluid than you take in and your body doesn't have enough water and other fluids to carry out its normal functions, dehydration may occur. You might suffer serious medical consequences if you do not replenish lost fluids in a timely fashion.
Intense bouts of diarrhea, vomiting, fever or excessive sweating are all common causes of dehydration. Inadequate intake of water during hot weather or exercise also may deplete your body's water stores. Although anyone is subject to dehydration, young children, older adults and people with chronic illnesses are all especially at risk. Mild dehydration may cause symptoms such as weakness, dizziness and fatigue. It is important to note that severe dehydration is a life-threatening medical emergency.
By increasing your intake of fluids, you can usually reverse mild to moderate dehydration. However, severe cases need immediate medical treatment. The safest approach is not to become dehydrated in the first place. Avoid dehydration by monitoring your fluid loss during hot weather, illness or exercise, and drinking enough liquids to replace what you lose.
Mild to moderate dehydration brings about symptoms such as a dry, sticky mouth, sleepiness or tiredness — children are likely to be less active than usual, thirst, decreased urine output — fewer than six wet diapers a day for infants and eight hours or more without urination for older children and teens, few or no tears when crying, muscle weakness, headache, or dizziness or lightheadedness
Severe dehydration symptoms include extreme thirst, irritability, confusion, lack of sweating, little or no urination, sunken eyes, shriveled dry skin, rapid heartbeat, fever, low blood pressure, delirium, and unconsciousness.
Treatment for dehydration
The most effective treatment for dehydration is to drink up and replace lost fluids. The best approach to dehydration treatment is to find treatment that suits your age, the severity of your dehydration, and its cause.
For children, consider giving them an oral rehydration solution to help replenish lost fluids. You can either buy this solution from a store or make a mixture yourself. Research on the Internet to find out how you can make your own rehydration solution.
In adults:

Adults that suffer from moderate dehydration can recover through drinking more water. Be sure to avoid coffee, tea, and other caffeinated beverages, as they increase dehydration.
Dehydration in athletes
Cool water is the best way to treat sports-related dehydration. A sports drink with electrolytes might also be useful. 
Treating severe dehydration
Severe dehydration in both children and adults should be treated by emergency professionals arriving in an ambulance or in a hospital emergency room, where they can receive salts and fluids intravenously rather than by mouth. Intravenous hydration provides the body with water and essential nutrients much more quickly than oral solutions do.