I get this as well.
I am on ADHD meds as well though, so it hits me harder.
Wake up feeling alright (as long as it's not too early) but as the day wears on, I go from being alright/ upbeat, to being agitated, highly anxious, dissociative, and then around 4pm every day it just goes from that to being really lethargic and melancholic. and then around 8pm after I have cried for a while, or just lay there staring, I am awake again and doing things. And can't sleep until waaaay later.
Like I'm awake right now, feeling depressed, agitated, really anxious, thoughts skipping everywhere, impulsive.. when I try to lay down, this all just turns into full blown anxiety. If I don't talk myself down before it hits, done for. Just will lay there freaking out for hours... eventually getting maybe 3-5 hours of sleep.
Sorry, I'm rambling. Anyways, if you want someone to talk to about this, you can talk to me... I think I know what you're going through.
(I actually called it "sundowning", referring to how alzheimer patients sundown... didn't realize that it was an actual thing.)