We all know the feeling.

我們都懂你的感受。

Irritable, groggy, and exceptionally lazy.

惱怒、頭腦昏昏沉沉的，還有非常地慵懶。

Chances are, you didn't sleep enough last night.

很有可能是你昨晚沒睡飽。

Or the past few nights.

或已經持續幾個晚上了。

But what exactly is enough sleep?

但是到底何謂「睡飽」？

And, more importantly, can you ever catch up on it?

更重要的是，你有辦法補回來嗎？

While the very function of sleep is still debated by scientists, we do know that it's necessary to function efficiently and productively.

雖然科學家們對於睡眠的作用還有爭議，不過我們知道睡眠是效率與生產力的必需品。

After all, we spend 24 years of our lifetime sleeping.

我們整個人生中共有 24 年的時間都在睡覺。

It had better be important.

因此睡眠一定很重要。

Researchers have tested how much is required each night by assigning groups of people to four, six, and eight hours of sleep over extended periods of time.

研究人員測試過每晚到底要睡多久才是足夠的，他們將測試者分成長期每晚睡眠 4、6、8 小時。

After 14 days, those with eight hours of sleep exhibited few attention lapses or cognitive issues.

14 天後，那些睡 8 小時的測試者們的結果顯示比較不會晃神，或認知不良問題。

However, those with six or four hours of sleep showed a steady decline.

然而，那些睡 6 或 4 小時的組別呈現持續下降的趨勢。

In fact, after only two weeks, the six hour group showed a similar reaction time to a person with the blood alcohol concentration of 0.1 percent, which is considered legally drunk.

事實上，只相隔兩週，睡 6 小時的組別和血中酒精濃度約 0.1% 的人的反應相似，被認定為所謂的「喝醉」。

The four hour sleepers suffered even more, occasionally falling asleep during their cognitive tests.

而睡 4 小時的測試者的痛苦則更加劇，偶爾還會在認知測驗時打瞌睡。

In both groups, brain function decreased day-by-day almost linearly, with no sign of leveling off.

這兩個組別的測試者，大腦的功能一天天地減弱，近乎直線性地下降，速度沒有減緩的趨勢。

Scientists have dubbed this cumulative effect as sleep debt.

科學家們稱這累積效果為「睡眠債」。

So can we recover from it?

可是我們能從中復原嗎？

After a night or two of little sleep, studies show that the body and brain can fully recover with a few nights of good sleep.

經過一或兩天的短時間睡眠，研究顯示搭配幾晚好眠後，人類的身體與大腦能完全復原。

However, with long term sleep deprivation, on the scale of weeks to months, the recovery of cognitive function is much slower, requiring many more nights of quality sleep.

但是長時間睡眠剝奪的話，從幾週到幾個月，認知功能的恢復期則需要更長久的時間，並需要更多的高品質睡眠。

On the time scale of months to years, it's unknown whether brain function could be fully repaired or if it causes permanent damage.

日子再繼續延長的話，從月變成年計，我們無法預計大腦的運作是否能完全恢復或將造成永久性傷害。

Paradoxically, with chronic sleep deprivation, your sleepiness or how tired you feel does eventually level off, meaning that you become less and less aware of your objective impairment over time.

弔詭的是，睡眠長期被剝奪，你的睡意和疲憊程度最終會趨近於平穩狀態。意思是說，隨著時間過去，你愈來愈難察覺對腦部實際損傷有多少。

So how long should you sleep?

所以，你需要睡多長才夠呢？

Most studies tend to show that 7-8 hours of sleep is the average ideal for humans.

大部份的研究傾向於 7 至 8 小時為人類理想平均睡眠時間。

Apart from the cognitive issues, individuals who consistently sleep less than seven hours a night have an increased risk of heart disease, obesity and diabetes.

除了認知問題外，一個人若持續一晚睡眠少於 7 小時會增加患上心臟病、肥胖症，或糖尿病等風險。

Not to mention, a 12 percent higher risk of death.

更不必說會增加 12% 的死亡風險。

On the flip side, studies have shown that while sleeping more than eight hours does not impair brain function, it also carries an increased risk of heart disease, obesity, and diabetes, and a 30 percent increased risk of mortality.

從反面角度來看，研究指出睡眠超過 8 小時，並不會損害大腦運作，但它會增加心臟病、肥胖、糖尿病的風險，還有帶來多 30% 的死亡風險。

So too much sleep may also be a bad thing.

所以睡太多也不是一件好事。

But variation most certainly exists, and our genetics play a large role.

但是變異數是存在的，而我們的基因扮演相當重要的角色。

In fact, individuals genuinely unaffected by only six hours of sleep were found to have a mutation of a specific gene.

事實上，有發現不會因為只睡六小時而影響身體功能的人，他們都帶有某個特定的突變基因。

When scientists genetically engineered mice to express this gene they were able to stay awake for an extra 1.2 hours than normal mice.

科學家在小白鼠身上加入這種基因，牠們竟能比一般老鼠多清醒 1.2 小時。

It turns out these short sleepers have more biologically intense sleep sessions than the average person.

結果表示少睡者在生物學上有比一般人更深層的睡眠。

Ultimately, while it's important to know the ideal average of 7 to 8 hours exist, let your body and brain help you figure out its own needs.

最終，雖然我們知道理想的平均睡眠時間為 7 至 8 小時，但讓身體與大腦幫助我們了解自己的睡眠需求吧！

After all, no one shoe size fits all.

畢竟沒有一種標準能套用在全部的人。

If you want to know how to get better quality sleep each night in order to conquer the hurdles of sleep deprivation, we have some tips and research for you over on ASAP Thought.

如果想知道如何每晚擁有更好的睡眠品質，以克服因睡不飽而引起的麻煩，我們在 ASAP Thought 上提供幾個訣竅和研究。

You can find a link in the description below to that video.

你能在下面的說明連結裡找到這個影片。

Thanks to audible.com for giving you a free audio book of your choice at audible.com/asap.

感謝 audible.com 提供一本你自己選擇的免費有聲書，可至 audible.com/asap 參考。

Audible is the leading provider of audio books, with over 150,000 downloadable titles across all types of literature.

Audible 是有聲書的先驅提供者，它提供超過 150,000 個可下載的主題，並橫跨所有類型的文獻。

We recommend the A Song of Ice and Fire series, which the Game of Thrones TV show is based off of.

我們推薦《冰與火之歌》系列書籍，而影集《權力遊戲》是根據此書而來。

It's kept us up through the nights and caused a lot of lost sleep.

它讓我們熬了很多夜，犧牲很多睡眠。

You can download this audio book, or another of your choice, for free at audible.com/asap.

你可以下載這本有聲書，或上網至 audible.com/asap 擇你所愛。

And with a subscription, you get one free book a month, so you can read the whole series.

若你訂閱，將獲得一個月一本免費書籍，所以你將能免費閱讀到一整個系列的書。

Special thanks to Audible for making these videos possible.

特此敬謝 Audible 製作這些影片。

And subscribe for more weekly science videos!

記得訂閱收看更多每週上傳與科學有關的影片！