At the start of each cycle, you enter light sleep, then move into deep sleep, then dream, and finally move back into light sleep.

每個週期都是從淺眠開始，接著進入深眠，然後作夢，最後再回到淺眠。

These cycles take about 90 minutes each, and you feel most refreshed if you wake up at the end of the cycle, because by then, you are closest to your normal waking state.

一個週期大概是 90 分鐘，而如果在週期的最後醒來的話，最能消除疲憊，因為那是最接近自然醒的狀態。

To increase the chances of this, decide when you want to wake up, then count back in 90-minute blocks until you find a time close to when you want to fall asleep.

為了增加在週期尾端醒來的機率，你要先訂一個起床時間，然後以 90 分鐘為單位往回數，直到找到一個接近你上床入睡的時間。

So let’s imagine you want to wake up at 8 AM.

那我們現在來假設你想要早上八點起床。

Chunking back in 90-minute blocks would look like this.

像這樣，以 90 分鐘為一個單位逆時針往回數。

And so you should aim to fall asleep around either 11 o’clock, or half past 12 at night.

所以你的目標應該是在 11 點或是晚上 12 點半入睡。

And so if you want to wake up feeling especially alert and refreshed, simply follow the 90-minute rule.

如果你希望起床時能神輕氣爽，就遵循這 90 分鐘原則吧！