Hello Boris & Welcome to the BB forums.
Life can be so complex at times that we really don't know what's happening to ourselves. Being in a retirement village as you had mentioned with many there undergoing dementia can also an detrimental affect in your own personal well-being. Being in that type of environment is often very stressful.
There's a number of different types of dementia which a sufferer can ungo dramatic changes in their personality without being aware of it themselves. Those around them can also be subconsciously affected by their behaviours. Your thought patterns are sitting in your subconscience mind & often releases the stress in the form of dreams.
Seek out a good reputable psychologist who you can have a Talk Therapy with about your concerns. They will be able to explain into detail why these nightmares are happening to you.
No, Boris, I don't think you're in transition of going into dementia, yet it would be a very good idea for you to see your local Dr whom you feel comfortable discussing some of those issues. From there on the Dr may refer you to psychologist or just having a Talk with him/her.
Having a good face to face talk about your concerns will help you in so many ways.
Hope this post is of some comfort to you & wish you all the best.