Dreams are necessary to survival. I believe they consolidate recent experiences into a highly structured memory in a way that's meaningful to us. People don't necessarily remember their dreams. Dreams are symbolic and can be interpreted usually. It's not uncommon to be disturbed by the images but it's best to just accept a dream as something you went through and now is over and to forget it, unless you specifically want to try to analyze it for meaning. If you keep having the same dream over and over again that is similar to PTSD like Mark said but you don't seem to have gone through as traumatic an experience as someone in combat etc.