Stress can make existing problems worse. In one study, for example, about half the participants saw improvements in chronic headaches after learning how to stop the stressproducing habit of “catastrophizing,” or constantly thinking negative thoughts about their pain. Chronic stress may also cause disease, either because of changes in your body or the overeating, smoking and other bad habits people use to cope with stress. Other forms of chronic stress, such as depression and low levels of social support, have also been implicated in increased cardiovascular risk. And once you're sick, stress can also make it harder to recover. One analysis of past studies, for instance, suggests that cardiac patients with so-called “Type D” personalities — characterized by chronic distress — face higher risks of bad outcomes.