A client in the emergency department is hyperventilating and says: 'I can't breathe — I'm dying.' Vital signs are: RR 32, SpO2 98%, HR 102. What is the most likely cause and appropriate nursing response?

PANIC ATTACK WITH HYPERVENTILATION: CLINICAL PICTURE: SpO2 98% confirms adequate oxygenation (true respiratory emergency would show declining SpO2); rapid rate is from anxiety, not hypoxia; patient is ventilating EXCESSIVELY (not insufficiently); HYPERVENTILATION PHYSIOLOGY: Blowing off CO2 causes respiratory alkalosis → cerebral vasoconstriction → lightheadedness, tingling, chest tightness → increased fear → more hyperventilation (vicious cycle); MANAGEMENT: Stay with the client; calm, unhurried presence; speak slowly and quietly; reassure about SpO2 ('Your oxygen level is perfectly normal'); coach slow diaphragmatic breathing (inhale 4 counts, exhale 6 counts); do NOT use paper bag over face (outdated, can cause hypoxia); rule out medical causes (pulmonary embolism has similar presentation but SpO2 would be declining); obtain 12-lead ECG to rule out cardiac cause; anxiolytic may be ordered; COMMUNICATION: Never say 'you just need to calm down' — this is dismissive and escalates anxiety.