This TED-Ed lesson from our archive features educator Claudia Aguari.

In 1965, 17-year-old high school student Randy Garner stayed awake for 264 hours.

That's 11 days to see how he'd cope without sleep.

On the second day, his eyes stopped focusing.

Next, he lost the ability to identify objects by touch.

By day three, Garner was moody and uncoordinated.

At the end of the experiment, he was struggling to concentrate,

had trouble with short-term memory, became paranoid,

and started hallucinating.

Although Garner recovered without long-term psychological or physical damage, for others,

losing shut-eye can result in hormonal imbalance, illness, and in extreme cases, death.

We're only beginning to understand why we sleep to begin with, but we do know it's essential.

Adults need seven to eight hours of sleep a night, and adolescents need about 10. We grow sleepy

due to signals from our body telling our brain we are tired, and signals from the environment

telling us it's dark outside. The rise in sleep-inducing chemicals, like adenosine

and melatonin, send us into a light dose that grows deeper, making our breathing and heart rate

slow down, and our muscles relax. This non-REM sleep is when DNA is repaired, and our bodies

replenish themselves for the day ahead.

In the United States, it's estimated that 30% of adults and 66% of adolescents are regularly

sleep-deprived. This isn't just a minor inconvenience. Staying awake can cause serious bodily harm.

When we lose sleep, learning, memory, mood, and reaction time are affected.

Sleeplessness may also cause inflammation, hallucinations, high blood pressure, and it's even

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