Dream

http://en.wikipedia.org/wiki/Dream
When we get into a deep sleep, sometimes there will be some visualize that keep on playing in our mind. in my own experience, i felt such i was acting in a challenging movie. sometimes it is fun but sometimes it is really scary untill i have to burn the midnight oil for the whole night. actually it is just a dream. the scientific study of dreams is known as oneirology. General observation shows that dreams are strongly associated with rapid eyes movement (REM). so, what ever it is, we shouldn't be afraid because it is just an entertainment of sleep..