Heat exhaustion is a milder condition than heat stroke.
Both conditions occur most often on hot days during physical activity. Anyone can have either condition, and either condition can happen to older people even during such mild activity as taking a walk. In heat stroke, the person's temperature control system that causes sweating stops working correctly. The body temperature rises so high that brain damage and death will result if the person is not cooled quickly. There may be dizziness, nausea, headache, rapid pulse, and unconsciousness.