Preoccupation with fears of having a serious disease is called?

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E6 Medicine Davidson Principles Practice 24e p. 1222-1224
E6 Kaplan Sadock's Synopsis of Psychiatry-2022 (pp 1-3768 of 3768) pp. 1448-1450, 1441-1443
Practise the full RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016
Attempt every question from this paper in a timed mock, then review the full solution for each one.