Hypochondriasis or hypochondria is a condition in which a person is excessively and unduly worried about having a serious illness. It has been claimed that this debilitating condition results from an inaccurate perception of the condition of the body or mind, despite the absence of an actual medical diagnosis. An individual with hypochondriasis is known as a hypochondriac. Hypochondriacs become unduly alarmed about any physical or psychological symptoms they detect, no matter how minor the symptom may be, and are convinced that they have, or are about to be diagnosed with, a serious illness.

Source: Wikipedia