: 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

Funny you should ask:

Before the wide spread use of artificial lights, there was a first sleep and a second sleep. Some scientists believe that “bi-modal” sleep is what humans are most accustomed to.

Until the early 18th century, people would go to bed more or less at sundown. They would then wake up in the middle of the night and spend an hour or so thinking, praying, reading, making love, etc. Then they would go back to sleep for another few hours.

Here is an article providing more in-depth information about first sleep, second sleep, and the 8 hour sleep:

[https://www.bbc.com/news/magazine-16964783](https://www.bbc.com/news/magazine-16964783)