This comment is prompted by Sukratu's comment on my previous posting. He seems to have concluded from my blog that I suffered from a "psychosomatic illness". I'm not aware that this conclusion can be unambiguously drawn from what happened to me in recent times, but am prepared to consider that it's a possibility. In looking for some information on disorders or illnesses of this type, I came across several somewhat distinct classifications.
Lowest on the scale of respectability is the factitious disorder. This is diagnosed when "a person acts as if he or she has an illness by deliberately producing, feigning, or exaggerating symptoms". In short, the patient is faking the illness.
A somatoform disorder is a physical disorder that is entirely attributable to mental causes. One kind of behaviour that has recently been classified in this way is Munchausen Syndrome, in which "those affected feign disease, illness, or psychological trauma to draw attention or sympathy to themselves". This looks identical to the definition of factitious disorder above, but for one crucial word: "deliberately". In fact Munchausen used to be considered a factitious disorder and sufferers of this syndrome were contemptuously called "frequent flyers" (because they would be frequently in hospital) but after its reclassification as somatoform, they can take comfort that their problem is "not the result of conscious malingering ... sufferers perceive their plight as real" (from the Wikipedia link above).
Psychosomatic disorders are higher on the scale of respectability. Wikipedia tells us that "Some physical diseases are believed to have a mental component derived from the stresses and strains of everyday living. This is the case, for example, of lower back pain and high blood pressure, which appear to be partly related to stresses in everyday life. Psychiatry has found it difficult until relatively recently to distinguish somatoform disorders, disorders in which mental factors are the sole cause of a physical illness, from psychosomatic disorders, disorders in which mental factors play a significant role in the development, expression, or resolution of a physical illness."
In other words, if its purely your fault then it's somatoform but if there's already a problem and your attitude is just making it worse, then it's psychosomatic. However it's important to point out that lay people usually understand "psychosomatic" to have the meaning given above to "somatoform", the latter word being quite unknown in common parlance.
Now what bothers me as a scientist is that the categories above are poorly defined, and classifying a patient into one of these categories is also an ill-posed problem. As the Medscape webpage on conversion disorder (a type of somatoform disorder) puts it, such disorders tend to be diagnosed when "symptoms of an organic medical disorder or disturbance in normal neurologic functioning exist that are not referable to an organic medical or neurologic cause". In other words, if we don't know what caused it then it must be mental in origin. Or as Wikipedia in a rare burst of humour puts it, "I can't cure you: you must be mad".
It's perfectly possible that things not currently understood by medical practitioners are not "psycho-" anything, but due to a very specific external cause. A prime example is the peptic ulcer. Long thought to be caused by emotional stress, it turned out to be in fact caused (in 70-90% of cases) by helicobacter pylori, a discovery that won a Nobel Prize in 2005 for Barry Marshall and Robin Warren. In a well-known story, once he was convinced of his theory Marshall actually swallowed the contents of a petri dish containing the bacterium and rapidly started to develop an ulcer. Since helicobacter is quite easily cured by an antibiotic, patients with ulcers are now treated with antibiotics (as was Marshall). Quite a change from what was done to me when I had signs of a developing ulcer in 1984. Then, doctors looked at me strangely and kept asking me to calm down and take it easy. They were pleased to notice that I was irritable (as anyone would be who had a constant nagging pain in the abdomen) since it confirmed the prevalent theory at the time. No one offered an antibiotic, since the result leading to the 2005 Nobel Prize was far in the future.
But the ulcer story doesn't end there. Recent studies still support the notion that "psychological factors do play a significant role" in the development of ulcers. The role is somewhat indirect, as helicobacter thrives in an acidic environment and stress can increase the production of stomach acid. In other words, to get an ulcer it helps to have both (i) helicobacter in your stomach, (ii) acid, possibly due to stress, in your stomach.
So if you scroll up you will see that ulcers remain "psychosomatic" by the definition I gave, namely that there's already a problem and your attitude has made it worse. But even this is rather facile. Emotional stress is not the only way to get excess acid in your stomach. You could be obliged to have irregular meals and/or irregular sleep times due to your job. Or just be starving due to poverty. All these will make you acidic and give any helicobacter inside you a pleasant environment in which to grow. Therefore the correct way to treat an ulcer is first to administer medication and second look into the causes of excess acidity if any.
This could also become the way to treat dystonia, irritable bowel syndrome and ulcerative colitis in future. The cause of none of these is known today, but all have long carried the psychosomatic or even somatoform label. As an example, this research paper from 1950 finds ulcerative colitis to be closely associated with neurosis and this blog article recounts how it was related to schizophrenia! Today, however, genetic and environmental factors are being widely discussed in the context of UC, while both dystonia and IBS are being associated with problems in the basal ganglia of the brain.
So finally, is it your mind or your body or both? The best answer I can give is that it's always both. But telling the patient to calm down is never the first line of therapy.