Your father needs to have a complete neurologic workup that includes bloodwork, MRI of the brain, MRA of the vessels of the head and neck, carotid artery ultrasound and possibly even an echocardiogram. This is the standard testing done for stroke and if it hasn t been done in some time, it should certainly be repeated. Consulting with a good neurologist whose practice centers around stroke is a must, because the neurologist will help your father to control stroke risk factors that will help him to prevent another such event from happening. I hope this information has helped you and that he feels better.