A 45-year-old woman presents to the emergency department with a severe headache and nausea. Her blood pressure is 230/128 mm Hg. She is alert and oriented with a normal neurological examination, normal fundoscopy and creatinine 85 µmol/L. ECG and troponin are normal. There is no dyspnoea, chest pain or evidence of acute end-organ damage. What is the most appropriate immediate management strategy?