Exhaustion and dehydration

When the body loses more fluid than it replaces, blood volume can fall and the heart may work harder to circulate blood. This can produce tiredness, headache, light-headedness, dry mouth and concentrated, dark urine. Vomiting or diarrhoea, heat exposure, fever, heavy sweating and difficulty drinking are common routes to dehydration. A urinary infection, kidney stone or gastroenteritis can also cause fluid loss or make drinking difficult, so pain, fever or ongoing bowel symptoms change the urgency.

Move to a cool place and rest. Take frequent small sips of water or an oral rehydration drink, particularly after vomiting or diarrhoea. Continue light food as tolerated; soup or other fluid-rich foods may be easier than a large meal. Avoid alcohol, and do not rely on very sugary drinks. Monitor whether your mouth feels less dry, dizziness settles and urine becomes more regular. If you have heart, kidney or liver disease, ask a clinician how much fluid is appropriate.

Seek urgent care for confusion, fainting, severe weakness, inability to drink, repeated vomiting, severe abdominal pain, blood in vomit or stool, or very little or no urine. Heat exposure with confusion or collapse is an emergency. Contact a clinician when exhaustion does not improve after fluids, or when fever, painful urination, flank pain or persistent diarrhoea is present.

Record when the fluid loss began, whether vomiting, diarrhoea, sweating or fever is involved, and any change in urine. Ask whether oral rehydration is suitable, whether medicines may worsen fluid loss, and whether urine or blood testing is needed.