Yes, all animals sleep, that is they experience rapid eye movement and non-rapid eye movement sleep. That isn't to say that all creatures sleep — all mammals and birds sleep, to be specific. There are more than 700,000 species of insect, however, and there's no evidence that any of them experience REM sleep.
More sleep facts:
- Only some amphibians sleep. For example, the tree frog sleeps, but the bull frog does not.
- Sleep debt is the term used when one doesn't get enough sleep. Lack of sleep can result in minor issues, such as lack of concentration, but it can also result in more major issues such as fatigue, illness and even early death.
- The Romans and Egyptians had a trick to get to sleep — not the warm milk modern mom's might use, but lettuce.
- Not all creatures sleep lying down. Horses and giraffes can sleep standing up, but even they must lie down for REM sleep. Bats sleep while hanging upside down, and some marine animals and some bird species can sleep with only one half of their brain, leaving the other half alert.
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