Falling asleep does not turn you off. Your brain and body keep working while you sleep.

Sleep comes in two types. Non-REM sleep goes from light to deep. REM sleep is when most dreaming happens. REM stands for rapid eye movement.

In deeper sleep, your heart and breathing slow down. Your body temperature drops.

In deep sleep, it is harder to wake someone up.

The most vivid dreams happen in REM sleep. Your eyes move quickly under your eyelids.

Dreams are pictures, thoughts or feelings that come to us as we sleep.

Your body makes growth hormone during sleep. It helps bones and muscles grow. Sleep helps children grow.

Animals need sleep too. Dolphins sleep with only half of their brain at a time. That way they can stay aware of danger.

Children from 6 to 12 years old need 9 to 12 hours of sleep a day. Most healthy adults need 7 to 9 hours each night.

Light from phones, tablets and other screens at night can confuse the body's clock. It helps to turn screens off 30 minutes before bed.

Words to know

• REM: dreaming sleep
• hormone: body helper
• vivid: bright and clear
• temperature: heat level