Fainting from heat and dehydration

Sweating, vomiting, diarrhoea, fever, or simply drinking too little can reduce body fluid. Heat also widens blood vessels near the skin. Together, these changes can lower blood pressure, especially after standing. Thirst, dry mouth, headache, dizziness, dark urine, constipation, and unusual tiredness may accompany dehydration.

Fainting after fluid loss does not identify the cause by itself. Gastroenteritis and heat exhaustion can cause dehydration; urinary symptoms may point toward another problem. Repeated episodes deserve an assessment of medicines, blood pressure, heart rhythm, and kidney health.

Move the person out of the heat, lay them flat, and raise the legs. Cool the skin with damp cloths and airflow. Check breathing and do not give anything by mouth while they are unconscious, confused, or vomiting. When completely awake, offer frequent small sips of water or an appropriate oral rehydration drink. Avoid a rapid return to activity and stand only with support.

Emergency help is needed for delayed recovery, confusion, seizure, chest pain, breathing difficulty, severe weakness, serious injury, or inability to keep fluids down. Seek same-day care for very little urine, persistent dark urine, ongoing diarrhoea or vomiting, worsening dizziness, or another faint. Children, older adults, pregnant people, and those with kidney or heart disease may need earlier advice.

Ask which fluids suit you, whether medicines increase fluid loss, and whether tests are needed for blood pressure, electrolytes, kidney function, or an underlying illness. Describe recent sweating, bowel symptoms, urine changes, and the time needed to feel normal again.