<human>: Condense the text into a few key points

My grandmother, whose relationship to me has always been close & maternal, has been, until recently, an incredibly smart woman, quite funny (and she got way funnier as she got older), and very quick on the uptake. I've noticed nothing but positive changes in her personality & abilities since she retired in the mid-1990's. This held true when I was living nearby and seeing her weekly, when I lived at home as a child and saw her constantly, and when I was living out of state and seeing her only once or twice a year. Even as recently as 2013, when I moved home for about 8 months, I didn't notice anything amiss.  

But in the past 4 months or so, I've noticed that my grandmother is maybe not the quick-minded person she's been. She has to have us explain jokes to her sometimes if they have a lot of wordplay, and she talks like more of an average-intelligence person--repetition of facts that her audience already grasped, talking about really banal stuff, reverting to just being loving in lulls in conversation, even if we were kind of on a roll with an existing dialogue.  

It's hard to put into words, but it definitely seems like something is different about her, and in a negative way. I'm scared it's dementia, or another age-related mental problem. What can I do? No one else in the family (my husband, grandfather, brother, and mother) except my husband seems to have noticed at all, or at least no one has said anything about it to me.  

My grandmother was an RN for decades, and worked on a geriatric psych ward for 10+ years, so it's not as though she's unfamiliar with age-related mental changes, and I'm sure she wouldn't take offense if I brought it up to her directly. But should I be talking to someone else in the family? Is there something I should do to confirm that there's a real problem? Is there something else I should be considering?
<bot>: My grandmother seems to not be as quick as she once was, and I'm scared there's something medically wrong with her, but don't know what to do about it.