As scientists become increasingly able to probe deeper into our minds, they are beginning to shine some light on the mysteries of what happens when we sleep.
When your head hits the pillow, for many it's lights out for the conscious part of you. But the cells firing in your brain are very much awake, sparking enough energy to produce the sometimes vivid and sometimes downright haunted dreams that take place during the rapid-eye-movement stage of your sleep.
Why do some people have nightmares while others really spend their nights in bliss? Like sleep, dreams are mysterious phenomena. But as scientists are able to probe deeper into our minds, they are finding some of those answers.
Here's some of what we know about what goes on in dreamland.