Haha I know exactly what you mean!!
Have you heard of spoons theory for chronic illness/fatigue type conditions? The idea that performing everyday tasks cost "spoons" to the person and they only have a limited number of spoons each day, if they do more tasks than they have spoons, then it starts eating into the next day's allowance.
I think unmedicated ADHD can be a bit like this in that we can be a bit unaware of our own energy levels and so we can easily overdo it and then "steal" energy from the next day or even 2 days.
I think it's also a bit of a learned coping mechanism - if you know that getting started is absolute torture or like pushing an elephant up the stairs, then once you're going, you can't stop because of the fear that you might get stuck stopped. But that then causes us to ignore and perhaps even stop being aware at all of our internal signals that we are doing too much.
Time blindness factors in as well, I think. I tend to get into something and then not notice the time. I won't eat regularly so that likely doesn't help either.
Try keeping a log or tally of what you do over multiple days, and see if there is a pattern you can see. I would guess that what you're doing is a cycle, where you feel motivated so you get started on things, then you crash, then you feel bad, then you get motivated again, then crash again etc.
And this is much better for me since medication - I don't get so many of the "no energy for anything except scrolling" days, I'm more aware of time, I'm more able to have days which are more balanced between rest and activity. It's hard to learn this, though. I don't seem to know how to rest properly. I can only really rest when I'm totally exhausted and can't do anything else. I would like to work out some strategies for having a shorter recharge type break throughout the day.