Nodding off is dangerous. Some animals have evolved extreme ways to sleep in precarious environments

SCI--Extreme Animal Sleep - (ASSOCIATED PRESS)

Every animal with a brain needs sleep — and even a few without a brain do, too. Humans sleep, birds sleep, whales sleep and even jellyfish sleep.

Sleep is universal “even though it’s actually very risky,” said Paul-Antoine Libourel, a researcher at the Neuroscience Research Center of Lyon in France.