Mini-stroke is my guess, though it is only a guess. I worked with a woman who was about your father's age and she would occasionally get totally confused at work, not knowing the time or date or what she had done. It turned out that she was having tiny strokes. They don't cause any paralysis, mainly real confusion. It's been a long time since I was a nurse, but in your place I would call for a cab to take him to ER.