What does headache feel like with dehydration?

The pain may be felt across the head or behind the eyes and can become more noticeable when you stand, move, or exercise. Thirst, dry lips or mouth, weakness, dizziness, muscle cramps, and passing less urine may occur at the same time. Urine may look darker than usual, although urine colour is affected by several factors. Fluid loss from sweating, fever, vomiting, diarrhoea, or simply not drinking enough can contribute. A headache alone cannot establish dehydration, and a sudden or unusual headache needs separate attention.

Move to a cool place if heat or sweating contributed. Sip water regularly; if vomiting or diarrhoea has caused fluid loss, ask a pharmacist about an oral rehydration solution. Small, frequent sips may be easier than a large drink. Replace food as you feel able, and avoid alcohol while recovering. If you have kidney, heart, or other conditions that affect fluid balance, ask a clinician how much to drink rather than forcing fluids.

Get urgent medical care for confusion, fainting, marked weakness, inability to drink, very little urine, persistent vomiting, severe dizziness, or a headache that is sudden, severe, or different from usual. Seek advice if a child, older adult, or person with a long-term condition cannot replace lost fluids. Medical assessment is also needed when diarrhoea, fever, or vomiting continues or symptoms do not improve after drinking.

What may have caused the fluid loss? Is an oral rehydration solution suitable for me? How should my fluid intake change if I take diuretics or have kidney or heart disease? Which warning signs mean I should be assessed today?