第二，一旦完全进入睡眠状态，非快速眼动期间血液中的二氧化碳增加，氧气减少。

Second, once sleep is fully obtained, there is an increase of carbon dioxide and a decrease of oxygen in the blood that persists during NREM.

youdao

首先，睡眠者在半梦半醒及不同调节机制之间转换时进入睡眠状态，呼吸可能短暂地停止或减少。

First, there may be a brief cessation or reduction of breathing when falling asleep as the sleeper waxes and wanes between sleep and wakefulness and their differing control mechanisms.

youdao

在有些地方，例如巴厘岛和新几内亚，人们喜欢随时根据需要进入睡眠和醒来，白天时不时的打个盹儿，晚上却经常的爬起来不睡觉。

In places like Bali and New Guinea, people tend to slip in and out of sleep as they need it, napping more during the day, and getting up more at night.

youdao

You start off with a transition period when you're falling asleep. We call that stage I.

一开始是过渡期,你开始进入睡眠状态，这是第一阶段。

耶鲁公开课 - 心理学导论课程节选

Well, should we conclude, therefore, so nobody really believes that they're ever in dreamless sleep?

那么我们就应该得出结论，没有人真正相信,他们可以进入无梦的睡眠么？

耶鲁公开课 - 死亡课程节选

Then REM sleep emerges, rapid eye movement sleep.

这时就进入REM快速眼动睡眠。

耶鲁公开课 - 心理学导论课程节选