A hippo sleeping underwater automatically rises to the surface every ~4 minutes and breathes without waking.
23
Sea otters hold hands while sleeping so they don’t drift away from each other.
104
The record for the longest scientifically documented period without sleep is 264.4 hours (eleven days).
15
The average cat sleeps about 2/3 of the day.
203
Cows can sleep standing up, but they can only dream lying down.
745
The strangers in your dreams are actually people that you've seen in real life.
50
The human brain is more active during sleep than during the day.
28