What symptoms of high blood pressure require immediate medical attention?

Likely any.: Usually this is asymptomatic, but if you have headaches, epistaxis (nosebleed), blurred vision and a history of hypertension, you should see your doctor urgently, as these indicate severe hypertension. If there is no history of high blood pressure and you have these symptoms consistently, particularly if you have all of them, see your doctor immediately.

Headache, chest pain: The most concerning symptoms would include headache, chest pain, dizziness and shortness of breath. Additionaly the presence of any neurologic symptoms such as numbness, difficulty talking, weakness of an arm or leg.