Hans Selye was a Hungarian doctor who was the first person to identify stress as a medical issue and its effects on people. Known as the "father of stress research" he first developed his theory after observing how all subjects responded in the same way no matter what the stimuli or stressor was. Patients would exhibit some of the same symptoms no matter what the illness was.
He concluded that the patients were manifesting a physical response to negative emotions they were experiencing due to the stressor. Patients suffering from illness would commonly have what he called "diseases of adaptation", which were ulcers, high blood pressure, and heart attacks. He coined General Adaptation Syndrome to describe these physical effects that arose from the stress of an illness. When a patients fails to adapt or cope with the stress from the negative situation physical ailments (specifically the diseases of adaptation) would occur.