One article I read said that forgetting where you put your keys is normal, forgetting what the keys are for is dementia. Forgetting words or names is normal, forgetting what the words mean is less so.

With Parkinson's there can be a range of cognitive impairment, from fairly minor (can't do complex tasks like filling out tax returns) to major ones like hallucinations and delusions. But not everyone with PD has cognitive issues. If you are starting to be concerned, bring it up to your doctor. There are tests that can be done to see where you are mentally. Then they do them periodically to see if you are getting worse.

In one of my Neuro NP snippy moments she told me when I think I have Alzheimers I should let her know and she would prescribe something. My question is, if I had Alzheimers, would I know? As Kenneth saud, I may not know but those around me would. For me, I'm enjoying all I can for as long as I can and be my best self everyday. I won't let worries about a future I can't control steal my today.
Maria

The following info was copied from an article on the AARP website:
The terms “dementia” and “Alzheimer’s” have been around for more than a century, which means people have likely been mixing them up for that long, too. But knowing the difference is important.

In the simplest terms, one is broader than the other. If the two were nesting dolls, Alzheimer’s would fit inside dementia, but not the other way around. While Alzheimer’s disease is the most common form of dementia (accounting for an estimated 60 to 80 percent of cases), there are several other types.

You asked a great but very difficult question to answer. AARP provided a very simple explanation but is very limited in scope. Ginny provided a wonderful way to differentiate between the two.

My personal thought is that I try not to worry about the cause of my symptoms but focus on how to reduce their impact on my day. I do this because I don't want to lose focus on things that are out of control while i could be doing puzzles, games, PT, OT, etc to reduce how these changes impact me. There is so much that is unknown about the human mind so there is much even the experts are still learning so I'm letting them figure out the name and the why while I work on the how do I manage the unwanted changes.
Making this change in my thinking has greatly reduced my stress, worry and anxiety and this reduction has allowed improvement of my memory.
Thanks for asking such a great question,
Maria

I'm not sure if you would know, but I bet those around you will.

The getting the words out is Parkinson I take speech therapy if you notice it seems to happen when you talk a little faster I jumble up the words and stutter and can't get words out