There are three “grades” of hydration – mild, moderate, and severe – which depends on the percentage of fluid and electrolytes your body has lost. Symptoms of dehydration generally become noticeable after 2% of our normal water volume has been lost. At this point you might feel thirsty, restless or irritable, decreased skin turgor, dry mucous membranes, decreased urine output, sunken eyes, sunken fontanel (the soft spot on the top of a baby’s head), and an absence of tears. These are all signs of mild to moderate dehydration.
In severe dehydration, people may develop diminished consciousness, hallucinations, lack of urine output, cool or moist extremities, and a fast or weak pulse.