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You might think that when we sleep we are completely unconscious and we have no idea what is happening around us. But that isn't quite true.

When we're sleeping, our bodies and brains are still working to keep us healthy and happy. We also still have some idea of where we are.

Read more: Curious Kids: What happens in our bodies when we sleep?

Our body knows how it is moving and where it is because of a sense called "proprioception". It's like a "sixth sense" that helps your body know where it is in the world and where all the parts of your body are in relation to each other.

When we are awake, this sixth sense stops us from walking into things or falling over.

You might think that it would switch off when we're sleeping. But because our bodies still work while we're sleeping, our sixth sense is still working too.

Even though we are asleep, we can still feel if we are comfortable and our sixth sense is working to let us know where we are in our beds. This helps us know not to fall out.

But the system doesn't always work very well when we are young. This is why kids fall out of bed sometimes.

We get better at this as we get older, so older children and adults are less likely to fall out of bed.

The different stages of sleep

Our sleep isn't the same the whole night through. It goes through different stages, from light sleep to deep sleep and back again.

One special stage of sleep, where we have our most exciting dreams, is called REM sleep. REM stands for rapid eye movement. That's when our eyes are moving around to try to see everything that is happening while we are dreaming.

During this stage, our brain sends a message to our body to stop moving to make it less likely we will get up or fall out of bed.

If our body didn't send this message to our brain, we would act out our dreams!

Message not recieved

Some people's brains don't send this message and these people do act out their dreams. This is called "rapid eye movement behaviour disorder". It is very rare.

There are stories of people with this disorder doing things like patting imaginary cats or hurting themselves by trying to jump out of bed while they're still asleep. Most of them wake up not knowing they did anything unusual until someone tells them.

Sleep is very important to help us grow big and strong. Our bodies and brains are still working while we are asleep to heal any injuries and help keep us happy and healthy.

Read more: Curious Kids: Where do dreams come from?

Hello, curious kids! Have you got a question you'd like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Author: Alex Agostini - Post doctoral research fellow, University of South Australia