therapy for seasickness of applying ice bags to the small of the back, and Darwin invited him to Down House to try out this therapy. In a manuscript dated 20 May 1865, thought to have been for Chapman, Darwin described his symptoms: In his autobiography of 1876, Darwin wrote of his illness, emphasising that it had been brought on by "the excitement" of socialising: Possible causes Medical science has tried repeatedly to pinpoint the etiology, and many hypotheses were made, such as: Asperger's syndrome or other Pervasive developmental disorder Chagas disease Chronic fatigue syndrome Crohn's disease Cyclic vomiting syndrome Lactose intolerance Lupus erythematosus Mast cell activation syndrome Ménière's disease Orthostatic intolerance Panic disorder with agoraphobia Obsessive–compulsive disorder Postural orthostatic tachycardia syndrome Posttraumatic stress disorder Psychosomatic disease Tick-borne disease Psychic causation Darwin found that his illness often followed stressful situations, such as the excitement of attending a meeting. Having escaped "smoky dirty London" to his country retreat of the former parsonage of Down House at Downe, he became increasingly reclusive, actually fitting a mirror outside the house, so that he could withdraw when visitors were coming around the corner. When he left, it was mostly to visit friends or relatives, though he did endeavour to meet his obligations to attend scientific meetings. Diagnosis of panic disorder and agoraphobia Barloon and Noyes report that as a young man, Darwin had "episodes of abdominal distress, especially in stressful situations". He had a "premorbid vulnerability" which was referred to as "sensitivity to stress of criticism in his youth". They contend that "variable intensity of symptoms and chronic, prolonged course without physical deterioration also indicate that his illness was psychiatric." Panic disorder usually appears in the teens or in early adulthood with an association with potentially stressful life transitions. The histories of panic disorder patients often include some type of separation from a person who is emotionally important to them, which may be significant as Darwin's mother died in 1817 when he was eight, though apparently Darwin had a happy childhood overall and was encouraged by his siblings. Bowlby suggested that separation anxiety may help cause the development of panic disorder in adulthood and that agoraphobic patients frequently describe parents as dominant, controlling, critical, frightening, rejecting, or overprotective, which matches (disputed) descriptions of Darwin's father as tyrannical (see below). A study by Chambless and Mason says that regardless of gender, the less masculine in trait