Heat stroke is a serious medical emergency characterized by a dangerously elevated body temperature, typically above 104°F (40°C). Key symptoms include a throbbing headache, dizziness, confusion, lack of sweating despite the heat, hot, red, and dry skin, rapid heartbeat, rapid and shallow breathing, nausea, vomiting, muscle weakness or cramps, seizures, and loss of consciousness. Immediate medical attention is crucial, as heat stroke can cause organ damage, brain damage, and even death if left untreated.