Sleep pressure is built with movement, not with hours spent on the couch.

Yeah, this tracks with my experience completely. When I'm moving around during the day, even just walking to run errands or standing for most of the day at work, I fall asleep pretty quickly and actually feel rested in the morning. Spend a whole weekend barely getting off the couch and suddenly I'm staring at the ceiling at 1am wondering why my body won't shut off.

The sleep drive explanation makes sense to me. Your body builds up this pressure to sleep throughout the day, and physical activity seems to accelerate that. When you're sedentary, maybe that pressure doesn't build the same way, so you're lying in bed without actually being tired enough.

The timing thing is real for some people but I think it's overstated as a general rule. I've worked out at 9pm and slept fine. My brother can't do anything intense after 6pm or he'll be wired until midnight. Seems pretty individual.

As for what type of activity helps most, in my experience it's less about the type and more about whether I actually broke a sweat or spent significant time on my feet. A long walk does almost as much for my sleep as a lifting session. Yoga helps too but in a different way, more like it quiets the mental noise rather than physically wearing me out.

The log idea is smart. I did something similar for a few weeks and the pattern was hard to ignore. Sedentary day almost always meant worse sleep that night, sometimes with a oneday lag. Active day meant I was yawning by 10pm.