Apple’s sleep charts can feel like a nightly report card, and “core sleep” often ends up in the spotlight. Yet the science behind wearables suggests that fixating on that one stage is a distraction ...

What is core sleep is on your Apple Watch, and does it even matter? We look at which sleep stages matter most for quality ...

There is a stage of sleep where we still have a toe in the waking world — remaining able to take in outside information. Yet at the same time, the mind is unleashed and our thoughts flow more freely.

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