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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A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
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Studies show that the colder the room you sleep in, the more likely you are to have a bad dream.
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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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The higher someone’s I.Q. the more likely they are to be sleep deprived.
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The human brain is more active during sleep than during the day.
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