You don't have to climb Everest to feel it.
Above 26,000 feet, climbers forget their wives' names and make decisions they'd never make at sea level. At that altitude their brains are literally starved of oxygen. Yours may be too.
How does this show up?
That 2pm wall you hit every single afternoon.
The word you lose mid-sentence, right when you need it.
The paragraph you read three times before it clicks.
Feeling like someone you don't quite recognize anymore.