: Why is it recommended to have 8 hours of sleep when sleep cycles happen every 90 minutes, wouldn’t waking up at 8 hours be in the middle of your cycle?

Question

I’ve learnt a little about sleep cycles and remember that every 90 minutes is when we move through the 5 stages of sleep, but I’ve also heard it’s recommended to have 8 hours of sleep. Wouldn’t that make you feel drowsy if you’re interrupting the sleep cycle when you wake up after 8 hours?

In: Other

Answer 1

There’s three key ideas regarding your question.

The first is that humans generally need 7-9 hours of sleep. 8 hours is just an average.

The second is that sleep cycles average about 90 minutes. But…

The third is that as we get closer to waking up (assuming you have normal sleep and are not in sleep deficit) the cycles no longer enter deep sleep phases. Waking up in deep sleep is what makes us feel groggy most of the time.