I exercise a fair amount (run 80km a week). When I first started, I noticed I was more tired and slept better, now after doing it 10+ years I'd say I'm adapted and it has no effect. There's probably some better way of mixing exercises to reduce adaptation and keep getting tired (as well as the calorie burn, etc)

Also, I read that when doing more demanding training, in particular very long distances, it's possible to get into a "hypermetabolic" state where one doesn't sleep as well. Anecdotally I've felt this way after doing what for me are longer runs, say > 30 km.

I haven't experienced inability to think hard, even when I was doing more intense running. The more plodding kind I do these days I find is great for brain work as it lets me clear my mind of distractions and think about problems I'm working on. But it sounds like you are training harder than me