Perfectly sensible stuff, everyone knows that getting so fatigued when in the immediate presence of hungry wolves that you fall asleep, due to a massive increase in adrenaline is perfectly normal. Of course fatigue might have something to do with no longer being allowed to switch off. It's screens at work, screen 9n the commute, and screens at home till bedtime. Nah, couldn't be anything to do with that.
Aside from the psycho-nonsense issue, different brain activities have different effects on overall feeling. Playing a strategy game past 2:30 PM gives me insomnia that night, but playing a first-person shooter game (mindless shooting of zombies) doesn't. Maybe some neurons deplete something or accumulate something in specific parts of the brain, or maybe their helper cells are slow to recover from their efforts. Someday they may find the physical basis for such things.