A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
23
The human brain is more active during sleep than during the day.
28
The record for the longest scientifically documented period without sleep is 264.4 hours (eleven days).
15
One reason that kittens sleep so much is because a growth hormone is released only during sleep.
212
People who sleep late have more mental stamina and can outperform early risers.
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