Research suggests that the run-of-the-mill bad dreams (which may be most of them) are actually good for your brain. Bad dreams allow you to process and regulate the day's emotions during REM sleep, when dreams occur.
Such dreams are commonly filled with bizarre and possibly scary images, which allow you to dispel fears.
However, these dreams differ from nightmares, which are bad dreams that wake you up. Nightmares reveal a problem in emotional processing. While waking up from a nightmare is a relief, it may serve to reinforce the feeling that the threat was real. About 85 percent of people have one nightmare a year.