A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
23
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.
15
The higher someone’s I.Q. the more likely they are to be sleep deprived.
29
Honeybees never sleep.
276
Bats sleep 18-20 hours per day.
5
The record for the longest scientifically documented period without sleep is 264.4 hours (eleven days).
15
Cows can sleep standing up, but they can only dream lying down.
745