If you've ever had a nightmare, you're in good company. Almost everyone gets them once in a while — adults, as well as kids. A nightmare is a bad dream. It can may make you feel scared, anxious, or upset, but nightmares are not real and can't harm you.

While you sleep, your brain doesn't just turn off. It goes through several sleep stages, including REM, or Rapid Eye Movement, sleep. Why do they call it that? Because during this stage of sleep, your eyes move back and forth under your closed eyelids. During REM sleep, you have dreams and sometimes those dreams can be scary or upsetting.

About every 90 minutes your brain switches between non-REM sleep and REM sleep. The amount of time spent in REM sleep increases with each sleep cycle through the night. The longest periods of REM sleep occur towards morning. If you wake during this REM stage, it is easier for you to remember what you were dreaming about. That's why your most vivid dreams — and nightmares — occur in the early morning hours.
Why Do you Get Nightmares?

Stressful things that happen during the day can turn dreams into nightmares. Nightmares may be a way to relieve the pressures of the day. This usually means dealing with things most kids have to face at one time or another: problems at home, problems at school, and stress from sports or schoolwork. Sometimes major changes, such as moving or the illness or death of a loved one, can cause stress that leads to nightmares.

Another thing that may cause nightmares is watching scary movies or reading scary books, especially before you go to bed.

Sometimes if you are sick, especially with a high fever, you may have nightmares. Certain medications also can cause nightmares. Let your parents and doctor know if you notice you are having more nightmares around the time you started a new medicine.

But sometimes you might have a nightmare for no reason at all.