Hello Katie, thanks for asking about it. Headache on the side you mentioned is seen frequently in the uncontrolled blood pressure. It is good to check with his doctor about. Sudden knee swelling can be seen in psuedogout which could also be with hypertension
or other chronic diseases in the elderly. Sudden knee swelling could also be due to an infection of the knee which could be as a result of urinary infection or other infections. He should talk about these issues with his doctor. Best wishes.