I work with AI tools all day. Research, drafts, code: AI makes the first pass, and I review and fix it.

Some days a work document just won’t go in. I reread the same sentence a few times and nothing sticks. Must be tired, I figure, and move on.

Then five minutes later an interesting conversation snaps me right back.

If I were actually tired, the conversation should have felt just as foggy. It didn’t, and that’s the strange part.

The “empty tank” story doesn’t hold up

The usual explanation: you have a fixed amount of mental energy for the day, and once it’s spent, you’re done. But that story can’t explain snapping back to full clarity mid-conversation. An empty tank stays empty.

Research on mental fatigue tells a different story. In one 2.5-hour repetitive-task study from 2015, raising the reward partway through made the same people’s fatigue drop and their performance improve. A boring task does the opposite: it produces strong tiredness and reluctance on its own, but a 2008 study on vigilance-type tasks shows that subjective fatigue doesn’t reliably track with how much performance actually drops.

So the brain isn’t one battery. Sleepiness, overload, plain dislike of the task, boredom, and overstimulation are different problems that all look the same from the outside: fog.

Treat all five as one thing and the fix is always “rest.”

Working with AI all day makes the mix-up worse

The easy, well-defined work goes to the AI tools first. What’s left for you is review, judgment calls, reading things where the answer isn’t obvious. That’s exactly the kind of task most likely to produce boredom or resistance fog, not real exhaustion.

But when the AI has handled most of the typing and the research, “I worked a lot today, I’m wiped” is still the easiest story to reach for at the end of the day. What actually ran out usually isn’t stamina. It’s the supply of judgment calls you had to keep making.

Get the cause wrong and the fix runs backward: meditating to calm down when you’re actually sleepy, or pushing through when the real problem is resistance.

A 30-second check before you rest

When the fog hits, sort the cause before you do anything about it.

  • Heavy eyes, yawning: you’re sleepy. Get some sunlight and move, or take a short nap.
  • Rereading the same line: you’re overloaded. Dump what’s in your head into a note and cut the scope to one thing.
  • Everything else sounds more appealing than this one task: you’re resisting it. Write one line on why it matters, then focus on it for five minutes.
  • Itching to switch screens: you’re bored. Slow down and stay with one thing.
  • Thoughts racing but narrow and impatient: you’re overstimulated. Cut the input and slow your breathing.

If five minutes of the right fix doesn’t clear it, take a real break: twenty minutes or so. How you rest follows the cause too. If it’s not sleepiness, resting means a walk or light movement, which a 2021 study found edges out watching TV for getting your head and motivation back. If it is, resting means a short nap. Five and twenty minutes are starting points, not the answer.

One thing to skip during those twenty minutes: Reels, or any recommended-content feed. Switching between short clips increases boredom instead of relieving it, a 2024 study found. Participants expected switching to help and got the opposite. Whatever you were doing also takes longer to get back into once you’ve been somewhere else.

How I set up the day

Diagnosing the fog handles the moment. There’s also a slower layer: how the day is set up so less of it happens in the first place. Working through this, here’s what I’d prioritize first.

Mornings start outside, before the feed. I get outside for fifteen to twenty minutes right after waking, before opening anything. A 2022 meta-analysis found that enough bright daylight measurably helps alertness.

The post-lunch slump isn’t a malfunction. Sleep pressure builds through the morning and naturally peaks around midday regardless of what you ate, so changing your lunch doesn’t make it disappear. The fix is not scheduling your hardest calls into that window.

When there’s another focus block in the evening, the temptation is to push through on coffee. But that cup cuts into the night’s sleep, and the next morning starts foggy. A 2023 meta-analysis found that on days with caffeine, people actually slept 45 minutes less on average: about 9 minutes longer to fall asleep, 12 more minutes awake during the night, and 11 minutes less deep sleep. A cup of coffee (about 107mg) needs roughly 8.8 hours before bedtime to avoid that loss. So coffee stops in the early afternoon, and evening work runs without caffeine.

Next time the fog hits

Nobody stays sharp all day. The fog will come. Check one thing before you rest: is this sleepiness, or is this resistance.