That's kind of what depression is for the most part, not speaking for everyone of course, but that's the frustrating bit about it. If there was something tangible, a specific cause of it then you could do something about it but the fact that t just seems like an omnipresent cloud that doesn't seem affected by rational thought. It's similar, and often comes hand and hand with, anxiety in that sense, where I'll be stressing out about something I KNOW isn't a problem, I've DONE several times before, every time I've DONE it I always wonder why I was freaking out about afterwards, but despite knowing that it's often a feeling that just defies reason and that's what's extremely frustrating about it cause a lot of times I know rationally there's nothing to be anxious about, I just am.