Rachel is convinced that her occasional headaches are caused by a malignant brain tumor. although several physicians have assured her that she has no serious physical problem, rachel continues to seek medical attention for a brain tumor. her behavior provides an example of what

I believe that her behavior provides an example of Hypochondriasis.
Hypochondriasis is a condition in which a person is inordinately worried about having a serious illness. It is often characterized by fears that minor bodily or mental symptoms may indicate a serious illness, constant self-examination and self-diagnosis, and a preoccupation with one's body.