I think he would most likely be MORE truthful about his symptoms if he didnt feel threatened, and physicians (hopefully) are not threatening.
After reading the checklist I'm not so sure it's Alzheimer's, although certainly some points apply (they apply for me from time to time too). I do now agree that the physician is the way to go. He's sort of an old school person, and although I have no way of confirming it, he may have grown up thinking that mental illness is a sign of weakness. I do know he certainly doesn't understand it and there's a good chance that he thinks only "crazy" people see psychiatrists/psychologist.