The body responds physiologically to emotional stress. For example, stress can cause anxiety, which then triggers the autonomic nervous system and hormones such as adrenaline to speed up the heart rate and to increase the blood pressure and amount of sweating. Stress can also cause muscle tension, leading to pain in the neck, back, head, or elsewhere. The emotional disturbance that triggered the symptoms may be overlooked when the patient and the doctor assume that they were caused by a physical disease. Many fruitless diagnostic tests may be done to uncover the cause of the fast heart rate, headaches, backaches, and so on.
Psychologic factors can also indirectly influence a disease's course.
For example, some seriously ill people deny having a disease or deny its seriousness. Denial is a defense mechanism that helps reduce anxiety and makes a threatening situation more tolerable. If denial relieves anxiety, it may be beneficial. However, denial may prevent a person from complying with a treatment program, and this can have serious consequences. For example, a person with diabetes who denies the need for insulin injections and strict dietary management can have marked shifts in blood sugar levels and risks having complications such as diabetic coma.