So, if you stay awake or only sleep short periods of time, it's safer.

所以，如果你保持清醒或只睡很短的时间，这样会安全。

And those deep, slow-wave sleep periods are also reduced for people who have tied on more than one.

并且深度、慢波睡眠阶段也会因一杯以上的饮酒量而缩短。

Their sleep was not that different from ours. The range of sleep period was about 6.9 to 8.5 hours.

他们的睡眠时长和我们没有太大的差别，大概在6.9到8.5个小时左右。

It is fairly clear that the sleeping period must have some function, and because there is so much of it the function would seem to be important.

很清楚，睡眠必然具有某种作用。睡眠占去那么多时间，所以其作用似乎还是很重要。

Some studies have even shown that we have two distinct 4 hour natural sleep periods, which in the past would last between 8 PM-12 AM, and then again from 2 AM-6 AM.

一些研究甚至表明，我们有两个4小时的自然睡眠时间，在过去，一段时间会发生在上午8点至12点，另一段时间是凌晨2点至6点。