John's behavior may suggest that he has health anxiety, also known as illness anxiety disorder or hypochondriasis. Health anxiety is a condition in which a person becomes excessively worried about their health and develops an intense fear of having a serious medical condition, despite medical reassurance that they are healthy. People with health anxiety often monitor their bodies for signs of illness, seek frequent medical attention, and may engage in avoidance behaviors related to their health concerns. However, a proper diagnosis would require further assessment by a qualified mental health professional.