I have something similar. I don't know if it's a physical thing or not. I always wonder if it's because I hate facing my To Do list so much. I wake up expecting to either be in agony over not getting things done as usual, or will be miserable doing them.

In the evening, I don't feel so much pressure to do as much since it's either finished or I've determined to put it off til later. So my mindset likely contributes.

I also read that dopamine levels are lowered when you wake up but that was just some random thing on the internet and I have no idea if it's true....