🫩💤Sleep isn’t only about feeling…

From a post from Chris Williamson:

You don’t perform on 6 hours sleep.

One of the most important sleep studies ever ran a brutally simple test.

People slept 4h, 6h, or 8h per night for 14 days. No all-nighters. Just “normal” short sleep.

Cognitive performance was tested every two hours.

By day 14:

6 hours = same impairment as being awake for 24 hours.

4 hours = same as 48 hours awake.

But here’s the scary part – after day 3–4, people stopped feeling more tired.

Reaction times kept slowing, attention lapses kept increasing, working memory kept degrading.

But subjective sleepiness flatlined.

Your brain keeps getting worse, your ability to notice it breaks.

This is why chronic undersleeping feels sustainable – you adapt to feeling tired but you do not adapt to being cognitively impaired.

The participants would’ve told you they felt “okay”. Objectively, they were functioning like they’d pulled an all-nighter.

If you’re sleeping 6 hours and think you’re fine, you’ve probably lost calibration.

Sleep need is biological. Most adults need 7–9 hours.

“I only need 6” usually means “I forgot what normal feels like.”

Feeling fine is not evidence you’re functioning well.

Chronic sleep loss doesn’t just impair your brain – it blinds you to the impairment.

— h/t Aakash Gupta

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