Can someone tell me what the heck is Sundowners disease?

Yes, it's a behavior where many dementia patients get anxious, agitated and so forth as the sun is going down, hence it's called sundowning. They'll often ask to be taken home right away, where their children are, even where they're long deceased parents are, and that their parents are worried about them and they need to get home to them right away. Even if they are already home if they can see it getting dark out they will often ask to be taken home or to a long ago home where they once lived. They may try to wander or go out on their own at this time too to get to these goals.

It has not been well studied academically and they're not sure about the mechanism but interestingly one time during the middle of a bright summer day I put sunglasses on my Mom with Alzheimer's and although she'll usually take them right off she left them on for about 20 minutes and I noticed she started to exhibit the typical sundowning symptoms even though it was midday. When I took the sunglasses off she became calm shortly after.

I think it might be hard wired into all of us as a behavior that has an evolutionary advantage. It's a survival advantage to get home and nest and be safe well before it gets fully dark out. Those who didn't probably got eaten by predators :-) So I think this is hard wired into the ancient fear center of everyone's brain, the limbic system. In Alzheimer's brains they lose hippocampal and cortical brain function - the memory and also thinking rational parts of the brain. Without that part of the brain to keep the fear in check you unmask those fears in unnecessary situations. In healthy adults with a good cortex that can think and rationalize we control that fear and keep it in check.

Although some healthy parents will still insist their kids get home before dark :-)

A solution can be to reassure them and address the root fear. I found that emphatically looking at my mom and smiling and saying I have good news for you! Everyone that loves you knows you're right here and they can come find you anytime. Or saying we can wait right here everyone will be coming to meet us here in time. Or something like that.

Admittedly, as every care giver knows especially in dementia they can forget a few minutes later and incessantly ask dozens of times in an evening as the fear resurfaces...enough to try even the best patience. My mom was very repetitive but as the disease progressed the repetition has almost all gone away...replaced by new challenges.

Ask his doctor, Google it..

My mother sundowns really bad. She never knows where she is from day to day. Sometimes hour to hour. She has to be reminded daily because she always believes every afternoon that she has been taken to a different place or room. She has had to have her Xanax increased due to this. She gets very agitated in the afternoons and evening. It is rough. I was told my one doctor that I Just needed to deal with it by "entering their world" so to speak. Good luck!

It is not a disease; it is a cluster of symptoms that many persons with dementia exhibit repeatedly at about the same time each day. The most common time is at sundown, hence the name, but it could be every noon, or any other time of day.

The article juliapickett refers you to has helpful information.

https://www.agingcare.com/articles/sundowners-syndrome-133187.htm

It has to do with changing behavior and anxiety as the day ends and transitions to night.