What should you know about the results of dehydration?

When fluid loss exceeds intake, the body conserves water by making less urine, which may become darker and more concentrated. Reduced fluid in the gut can contribute to Constipation. Ongoing loss from vomiting, diarrhoea, fever, heat exposure, or heavy sweating can cause weakness, headache, dry mouth, and light-headedness. More serious dehydration may reduce blood flow to the brain and kidneys, causing confusion, fainting, or very little urine. Gastroenteritis and Heat Exhaustion are common contexts, but other illnesses can also cause fluid loss.

Replace fluids with frequent small sips, especially after vomiting or diarrhoea. An oral rehydration solution can help replace water and salts; follow the product instructions. Continue suitable foods as tolerated and rest somewhere cool if heat contributed. Monitor urine colour, urination, alertness, and ability to drink. Do not force large amounts quickly if vomiting continues. People with kidney, heart, or other fluid-sensitive conditions should ask a clinician how much to drink.

Seek urgent care for confusion, fainting, severe weakness, inability to keep fluids down, very little or no urine, blood in vomit or stool, severe abdominal pain, or signs of heat illness. Babies, older adults, and people with serious medical conditions can worsen quickly and need early advice. Arrange assessment if symptoms do not improve with careful rehydration or if dark urine persists.

What likely caused the fluid loss? Is an oral rehydration solution suitable for me? How should my usual medicines change while I am unwell? Which urine or alertness changes mean I need urgent care?