Nightmares become much more than bad dreams when they have a significant effect on your health and well-being. Among people who experience nightmares, those who are anxious or depressed are more likely to be distressed about the experience and suffer even more psychological ill effects. Although the relationship is not understood, nightmares have been associated with suicide. Because nightmares may have a significant impact on your quality of life, it's important to consult a medical professional if you experience them regularly. Sleep deprivation, which can be caused by nightmares, can cause a host of medical conditions, including heart disease, depression, and obesity. If nightmares in adults are a symptom of untreated sleep apnea or post-traumatic stress disorder, the underlying disorders can also have significant negative effects on physical and mental health.