Although we're not entirely sure why it is that we dream, there are many theories on the topic. One theory says that dreams go hand in hand with our emotions. During the day, our brains are too busy focusing on the tasks at hand to process all of our emotional responses. When we sleep, our brains don't need to focus on the external world, so we're left to work out the emotional side of things. For example, perhaps there have been rumors of downsizing at work. While you're there, you need to be professional and productive, so you put thoughts of losing your job on the backburner. Later, after you've fallen asleep, you dream that you're alone, wandering through a deserted town. Or perhaps you dream that you show up to work only to find that no one there knows you and your office is occupied by someone else. In this way, the emotions you couldn't mull over during the day are taking center stage as you dream.

New research has shown that it may be the sleep in which dreams occur that really helps to reset the day's emotions; the dreams simply run through them. Researchers at the Sleep and Neuroimaging Lab at the University of California, Berkeley, found that rapid eye movement (REM) sleep helps people better interpret positive expressions of emotions in others [source: Sharples]. Researchers also say that sleep deprivation can disrupt how we interpret and process emotional memories and magnifies our reactions to emotional events. On the other hand, they found that getting an adequate amount of REM sleep can help keep emotions in control [source: Walker]. It's during REM sleep that we dream, which allows the brain to run over the day and strip out the negative emotions from our memories. If you don't achieve enough REM sleep to dream and sort through emotions, the negative emotions build up and you can reach a constant state of anxiety, says Matthew Walker, director of the UC-Berkeley lab.