Psychosomatic disorders can generally develop when a stressful life event occurs, when someone experiences chronic stress, or when negative and self-sabotaging thought patterns persist over many years.
Different people may be affected in various ways by the same stressors. For example, one person may be particularly vulnerable to cardiac events and respond to a major stressor with heart disease. Another person may be susceptible to high blood pressure and respond to the same major event with a stroke. A third person may not get sick at all from the same event. It's not always easy to predict how stress will affect a person's health, but it's known that stress does affect a person's health and, therefore, it's important to practice regular stress management techniques. See the below resources for ideas on staying healthy.
Read more about psychosomatic conditions and stress.
This site has a wealth of information on stress and its effects, as well as stress management techniques. For more ongoing information and help from About.com Stress, see these stress management resources.