What I've personally noticed with prolonged untreated ADHD is that it makes me really really exhausted to basically just be awake, even if I don't do anything, and it only got worse and worse with age because of course priorities, responsibilities and overall health have changed. I only realised after I got the diagnosis and medication how draining it was to have adhd because you are constantly bombarded with outside stimulation you can't filter out (sounds etc) and always having to try harder than everyone else to just get really basic tasks done like making a sandwich and loading the dishwasher.