If you've ever been so thirsty that no amount of water seems to slake that thirst, chances are there is something going on inside your body that needs to be evaluated by a health-care provider. The headache might be caused by the unquenchable thirst and should be added to any list of symptoms you're giving. In isolation, any episode of thirst with headache might be benign, but if the episodes worsen or the headache is the worst you've had in your life, seek immediate emergency care as the cause could be life-threatening.
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Excessive thirst is one of the hallmark symptoms of diabetes. The thirst is caused by too much sugar in your bloodstream that your body can't convert to energy because of a lack of insulin, according to an article at MayoClinic.com. The symptoms of diabetes include excessive thirst, headache, frequent urination and blurred vision. You might have these symptoms intermittently as your body struggles to metabolize sugar, so it's important to be evaluated even if the symptoms aren't consistent.
Hypercalcemia is too much calcium in the blood. An article at "The New York Times" health site reports that it is most common in women older than 50 and is usually caused by hyperparathyroidism, an enlargement of one of the parathyroid glands that interferes with the metabolism of calcium. It can also be caused by disease of the adrenal glands or by getting too much calcium in the diet. Symptoms include muscle aches and fatigue.
Dehydration is probably the most common cause of excessive thirst and headache. Dehydration can lead to heat exhaustion and life-threatening heat stroke, so it requires immediate attention. Dehydration is usually caused by sweating or urinating body fluids and not replacing them. The first symptom that your body needs more fluid is thirst. This means, according to the the dehydrationsymptoms.com website, that your body has lost 1 percent of its fluid. At 2 percent, you'll start to experience anxiety and lack of appetite. When your body loses 6 percent of its hydration, you'll begin to lose coordination, and by 11 percent, you'll need to be hospitalized to restore your body to normal.