We just learned about Non-Rapid Eye Movement Sleep.
Let's learn about Stage 1 - Non-REM Sleep.
When you are falling asleep, there are thee steps called stages you go through.
The first one called stage 1 is sometimes called relaxed wakefulness.
The brain starts calming down, and sometimes muscles flex a little which are called hypnic jerks.
If someone fully wakes up, they might not even really think of this as sleep since it wasn't deep sleep, but it's stage 1 Non REM sleep.
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(from: wikipedia - non-rapid eye movement sleep)
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