Sleep is anything but a waste of time. While many people think of catching Zzs as the body “shutting off” until morning, nodding off actually activates a complicated process that helps you feel rested and healthy the next day. Scientists divide sleep into four stages — each full sleep cycle takes about 90 minutes to complete, meaning we cycle through roughly five rotations during 7.5 hours between the sheets. The amount of time spent in each stage of sleep varies by cycle, with more deep sleep taking place earlier in the night and more dreaming sleep in the second half of the night.
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