How long do our sleep cycles typically last during a normal night's sleep?

Our sleep cycles typically last usually 90 to 110 minutes on average.

Hey there,
Usually, REM sleep happens 90 minutes after you fall asleep. The first REM usually lasts for 10 minutes. Later each of your REM lasts longer and eventually it may last up to an hour. Thus, your heart and breath rate quickens

Hope this helps :))

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