Sleep may reinforce the negative emotions aroused by witnessing something scary or traumatic. As a result of "sleeping it off," you may be just as upset reviewing images of the event as you were in the first place. You can even have vivid flashbacks. But by staying awake after seeing, for instance, an accident or its aftermath, the emotional response to reviewing images of the event afterwards may be reduced, according to a new study from the University of Massachusetts, Amherst. The researchers tested out the well-worn assumption that sleep softens negative emotions aroused by a disturbing event or scene. The investigators asked their 106 young adult study participants to rate on a scale of one to nine their estimation of a picture (was it happy or sad?) and their personal responses (calm or excited). Some volunteers saw the first set of pictures late in the day and the second set after sleeping overnight; another group saw the photos in the morning and then again later the same day. The investigators found that those who had slept between viewings had the same emotional response on reviewing the images as they had the first time they saw the photos, while those who stayed awake had what researchers termed a "softened" response.