What should you know about dehydration sickness?

Fluid loss can follow vomiting, diarrhoea, fever, heavy sweating, hot weather or simply drinking too little. Thirst, a dry mouth, tiredness, headache, dizziness and passing less urine are common clues. Urine may become darker, although colour can also change for other reasons. Severe loss can affect alertness and blood pressure, especially in babies, older adults and people with ongoing medical conditions.

The illness causing fluid loss matters. Gastroenteritis can combine vomiting and diarrhoea, while heat exhaustion can cause sweating, weakness and nausea. Dehydration itself does not explain every symptom, so persistent pain, burning urine or blood in urine needs separate assessment.

Rest somewhere cool and take frequent small sips. Water may be enough for mild loss; an oral rehydration solution can replace water and salts when vomiting or diarrhoea has caused substantial loss. Follow the product directions and do not make it stronger than instructed. If nausea is present, sip slowly rather than drinking a large amount at once.

Once fluids stay down, return to light food as tolerated. Avoid alcohol, and limit drinks that worsen nausea. Keep track of whether you can drink and whether urine is becoming more frequent and lighter. Read about [Dehydration](/conditions/dehydration/) for broader guidance.

Seek urgent help if you are confused, faint, unusually drowsy, unable to keep fluids down, or passing very little or no urine. Get prompt medical advice for severe weakness, fast breathing, ongoing vomiting or diarrhoea, or symptoms after significant heat exposure. A child, older adult, pregnant person or someone with kidney, heart or endocrine disease may need advice sooner.

Ask what may be causing the fluid loss, which rehydration drink suits your situation, and whether medicines or an existing condition affect how much you should drink. Mention the timing of vomiting, diarrhoea, fever, urine changes and any dizziness.