Could be the weather ladydi. My daughter gets very sad after the time change, in the fall. Its dark by 5 pm here and she hates it.

You might want to look up Seasonal Affective Disorder. Hope this helps.

Could also be just from being tired. Sometimes when I'm exhausted I feel like a toddler who needs a nap- just want my teddy bear.

Yes, I get like that. I can have a good day or week and a the end of it I am tired and feel down. Almost like something is missing.

I have a couple thoughts on why but I don't really know if they are even in the ball park. lol

First I think it take a lot of effort for us with PTSD to have a good hour, day or week. It is tiring to keep your thoughts positive and cope with daily stresses. This effort makes you tired and when I get tired I get sad and depressed. I think for me it one of the causes of my sadness and depression is just being tired.

Second I do think the sadness and depression is from missing something. Again in my case I think this is a 2 part thing. First I believe I miss my old self, who I use to be and what I was capable of doing. I missing working and I kind of feel stuck with this person who is not really who I want to be. Second, my therapist told me this one and I think it is true, I have become so use to feeling awful that it just does not feel right to feel good. It has become a habit to feel bad. When I don't feel bad, I feel guilty and sad for not feeling bad. I actually miss feeling bad because it has become such a part of me.

Not sure if this makes any sense.

There is less daylight nowadays, as someone noted. The holidays are coming on, and that can bring sad memories or make us notice absences in our lives. For those with school schedules, whether as teachers or students, a big schedule change happens. It's hard to put a finger on just one cause, but you're not alone in this. I know what you mean.