Dehydration presents itself in a progression from thirst, fatigue, weakness, then delirium, coma, and finally death. Environment, such as temperature and humidity, will determine the rate of progression as well as hydration status when the dehydrating situation began. Thirst is a poor indicator of hydration. To return to normal hydration, we need to consume twice the amount of water it takes to quench thirst. Dehydration is a major contributing factor to fatigue, which can lead some people to turn to for food for energy.
Dehydration also leads to muscle cramps.
Certain medications can also act as diuretics, increasing fluid needs. Most of us know to drink water in the warm summer months. It is easy to do since we often look for relief from the hot outdoor temperatures with cool water. But the winter months don't lead to a decreased need for fluids. In the winter we are exposed to dry heat indoors and cold outside but are not apt to drink water.