The first thing he told me was that all sleep stages of sleep support your health and wellbeing, and there's not a lot you can do to control how long you stay in each stage every night.
You shouldn't rely on them to know how much REM or deep sleep you're getting or worry if your tracker says you're not getting enough... it will also be difficult to know if any changes you make to support potentially getting more deep sleep are actually leading to you getting more of it.
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