Some people have a "natural alarm clock" allowing them to wake up when they want. This is actually caused by a burst of the stress hormone adrenocorticotropin.
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One reason that kittens sleep so much is because a growth hormone is released only during sleep.
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There's a love mattress that is specifically designed for couples who sleep on each other's arms.
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Bats sleep 18-20 hours per day.
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Quick naps not only improve your alertness, but they also help in decision making, creativity and sensory perception.
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Cows can sleep standing up, but they can only dream lying down.
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Staying awake for 17 hours is the same for your body as drinking 2 glasses of wine.
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A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
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