Step 1: The defining feature described is a lasting preoccupation with the fear of having a serious illness (for example cancer or AIDS), built on the patient's own misinterpretation of normal physical sensations. An occasional change in heart rate, for instance, is read as evidence of heart disease.
Step 2: This is the hallmark of hypochondriasis (hypochondriacal disorder). The patient is preoccupied with the disease itself, the fear persists despite reassurance from normal medical assessment and investigations, and they move from doctor to doctor. Insight is usually present, the patient knows the fear may be unrealistic but cannot reduce the anxiety.
Step 3: The distractors differ. In somatization disorder the patient is preoccupied with multiple symptoms (at least 8 or more) rather than with one named illness. An obsession is a recurrent intrusive thought that the patient resists, seen in OCD. Conversion disorder presents with loss of motor or sensory function with no organic cause, not with fear of illness.
Conclusion: Preoccupation with a feared serious illness despite normal findings is hypochondriasis.