Vomiting and diarrhoea can lead to dehydration. Professional advice is important when fluids cannot be kept down or symptoms are severe or persistent. Children and vulnerable adults may need earlier assessment. This article does not specify medicine doses. Very little urine, worsening weakness, confusion or difficulty staying awake can indicate dehydration; severe signs require immediate assessment. Seek prompt help if fluids cannot be kept down, particularly for children or frail adults. Use oral rehydration products according to their labels and professional advice; do not improvise mixing ratios. Blood in vomit or sudden severe abdominal pain needs emergency care. This guide cannot grade dehydration.