Hypochondria

A mental disorder characterized by an excessive and habitual preoccupation with personal health and a tendency to interpret insignificant or imaginary conditions as evidence of serious disease; also called hypochondriasis.

Typically, hypochondriacs not only falsely believe that they have a serious disease (often, but not exclusively, of the heart or another internal organ), they persist in this belief even after being assured that they do not have the disease by a physician (or, usually, by many physicians). Hypochondriacs seem to have an increased sensitivity to internal sensations. It is also thought that serious childhood illness or experience with disease in a family member or friend may be associated with hypochondria, and that psychological stress in early adulthood related to disease or death may precipitate or worsen this condition.