I have SAD and this happens to me several times a day. Though it's not so much that it pops into my head, more that my train of thought leads me there by associ

I have SAD and this happens to me several times a day. Though it's not so much that it pops into my head, more that my train of thought leads me there by association. In a lot of ways SAD feels like a form of PTSD where instead of a single extremely traumatic experience, or many extreme experiences(known as complex PTSD), it's a huge amount of slightly traumatic ones. So it's sort of like a flashback. One of the things I've noticed is that when I'm on SSRIs and they're working(which has never been a long-lived state of affairs, unfortunately), this phenomenon is drastically reduced or even gone altogether.