A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
23
47% of people have a nightmare at least once a month.
186
The human brain is more active during sleep than during the day.
28
One reason that kittens sleep so much is because a growth hormone is released only during sleep.
212
Termites work 24 hours per day and they do not sleep.
57
The average cat sleeps about 2/3 of the day.
203