What can I do if I see a mental decline in my father-in-law?

If you can't get him to go to a neurologist - some elders think that means "mental health problems" and they resist - try to get him to his regular doctor for a checkup. Any excuse will do, whether it's his blood pressure or something else. Write the doctor a letter in advance stating your concerns. Once he is in front of his doctor, he may be more willing to take advice about seeing a specialist for, um, further information, or something. Coming on too strong about cognitive issues makes many people resist because they are afraid. For some reason, a routine issue can open the door. Not always, but sometimes.
Good luck,
Carol

Oh my gosh! This is MY Dad, too! He sees ants everywhere, and rodents (we don't). He has taken to holding on tight to nothing in his hand, except he doesn't know it's nothing. Yesterday, I woke him up and he grabbed his ear with one hand, and then that hand with the other and was struggling: "Get this dog off me!" No dog. he didn't even feel it was his own hand. The doctor suspects minor strokes -- we get an MRI this weekend. I got that test written by doing exactly what's suggested above: Wrote a BRIEF but punchy note to the doc, who read it before Dad went in. We have hidden his meds (so he can't take them) and the dogs alert us when he gets up in the night. But see what you can do to make sure he is safe if he does get up at an odd time. Good luck!!!!!!

I always thought this was a UTI, I would get him checked for that. Hallucinations mean infection when my Mom gets them. Her Urine culture are negative but the Dr treats anyway and it all goes away, hallucinations and craziness gone!! Good luck.