When I was in my 40s I noticed that if I was outside alone with nothing to divert my attention just before sunset, that I would often begin to have sad/apprehensive/agitated feelings.
This happened frequently for a long time if I was outside or even looked out.
I don't remember if I just stopped feeling like that or if it started another job and wasn't outside at that particular time??? I don't have an answer.
A few minutes ago I looked out a window and it happened again. Was the sun in the right angle? Were my younger feelings and feelings just now sundowning?
I don't have an answer.
This is to suggest that perhaps people who do sundown are experiencing the same feelings but aren't able to express them???
However, what you describe does make me think of another condition that my father suffers from: Seasonal Affective Disorder. It’s a condition that typically occurs in the winter months due to lack of sunlight that can cause depression. Depending upon what the weather was like and time of year when you had these experiences, this may be what you are experiencing.
https://www.mayoclinic.org/diseases-conditions/seasonal-affective-disorder/symptoms-causes/syc-20364651
Try and keep a log, recording dates, time of day, and weather and see if you can discern a pattern that you can then bring to a doctor.
If you are noticing sad, apprehension around sundown is it possible that it could be S.A.D. Also known as Seasonal Affect Disorder. These symptoms can be feeling depressed, loosing interest in activities, low energy, difficulty in concentrating. Usually these will not lead to challenging behavior. You also would have fewer symptoms in the summer when days are longer or if you are working inside in well lit areas where you would not be subjected to decreased light.