Ten things you never knew about dreams.

1. No one knows for sure why you dream—Doctors think dreams help people process the different kinds of "sensory input" that come in through the day. Some people have claimed experiencing eureka moments during dreams. Dreams are like an internal diary, sort of like a nightly commentary on your life.

2. You dream throughout the night, not just during REM sleep--Forget what you heard in college about dreams only happening during REM sleep. REM-sleep dreams are more common in the second half of the night and tend to seem more vivid and unrealistic. If you dream you jumped out of a plane and you saw rockets around you, that's almost certainly a REM sleep dream. Dreams during the first three of the four stages of sleep might seem les vivid.

3. You remember a dream if you awake during it--The major factor of whether you'll remember a dream or not is being awakened during the dream. If you don't wake up during the dream, the memory is gone. We're on a self-erasing tape while we're asleep.

4. Spicy foods might make you remember more dreams and nightmares--The meal makes it more likely you're going to wake up during sleep. The heavy meal has nothing to do with dream generation. It has to do with dream recall. In order to recall a dream, you have to be awake, at least for a few minutes. Our brain isn't able to convert from short-term to long-term memory while we're asleep.

5. You may be able to change bad dreams--Many therapists believe it's possible to "re-write" nightmares. People who suffer from post-traumatic stress disorder can train themselves to recognize when they're in a dream.

6. The brain is still hard at work while you're sleeping and dreaming--REM sleep isn’t a time of rest for the brain. The brain is being stimulated at an incredibly high level throughout dream sleep. That stimulation is what creates images in dreams.

7. It's hard to separate the function of sleep from the function of dreams--The function of sleep is to downscale things so that the brain is ready and able to learn the next morning. Dreaming is something the brain has to generate in the process.

8. Dreams may help people process and consolidate memories--Harvard researchers asked people to navigate through a 3D maze and then either nap for 90 minutes or stay awake but quiet. Nappers who said they dreamed about the experience got much better at navigating the maze.

9. Dreams do not foretell the future--Everyone wants dreams to be prophetic. But we always forget about the 500 dreams we had about phone calls that didn't come true the next day. All of these dream-related prophecies are just pure statistical phenomenon.

10. No one agrees about the meaning of dreams--Freud called dreams "the guardians of sleep." And he believed their purpose was to censor basic impulses, like aggression and sex. Some people think Freud was right, others think dreams have no meaning. And we should "treat it as a present."