The great thing about dream

I have no idea how dreams work. A dream is a succession of images, sounds or emotions that the mind experiences during sleep. The content and purpose of dreams are not fully understood, though they have been a topic of speculation and interest throughout recorded history. The scientific study of dreams is known as oneirology.(wiki)
My last night's dream seemed so real. I could feel it. My gosh! The real me, my real friends, my real teachers and the real scenario which could happen in the real world. Like I could have deja vu soon. *freak So, what was that? Some say you dream of somebody if you think about them right before you sleep. But that's not it. Because I have encounter lots of dream of somebody who have been out of my mind for long. I guess that's not true.
How should I count that dream? A nightmare? or A sweet dream? I don't know. But it definitely reminded me of home. I miss my family and friends :)