Dizziness when it is hot may be due to blood vessels dilating in hot weather, causing the patient’s blood pressure to drop. Severe blood pressure drop can cause impaired blood circulation, resulting in insufficient blood supply to the brain. Insufficient blood supply to the cerebellum and brainstem can result in dizziness, nausea, and vomiting, as well as balance disorders and ataxia. When the blood supply to the internal carotid artery system is insufficient, patients usually present with episodes of hemiplegic sensorimotor disorders and may also develop hemianopia. If a patient develops insufficient blood supply to the brain during the heat, he or she should usually drink more water and take rest. In addition, insufficient blood supply to the brain caused by heat may also be due to heavy sweating. When sweating heavily, it tends to cause a decrease in blood volume, which can reduce the effective circulating blood volume and cause hypoperfusion in the brain, resulting in discomfort such as dizziness in patients.