When a condition is psychosomatic, that means that it involves both the mind and the body. A psychosomatic illness originates with emotional stress or damaging thought patterns, and progresses with physical symptoms, usually when a person's immune system is compromised due to stress. A common misconception is that a psychosomatic condition is imaginary, or "all in someone's mind". Actually, the physical symptoms are real and can harm you as much as symptoms that originate from other means. (In fact, it's been estimated that over 90% of doctors visits are due to health problems influenced at least in part by stress, so psychosomatic illness is more common than people realize!). 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.
Classic psychosomatic disorders: ulcer, certain cardiovascular diseases, high blood pressure, eating disorders, chronic diarrhoea, rheumatism, certain skin diseases, abortion, allergy, etc.