Hello,, uncontrolled very high blood pressure can affect to blood vessels on brain may result in edema of surround tissue or bleeding due to high blood pressure or sometimes even thrombus clot in blood pressure, which results in damage to the neurons supplied by those vessels, which results in temporary transient ischemic attack to permanent stroke. So kindly consult a neurologist since he is having slurring of speech,, in early stages with treatment prognosis is always better.