A 45 yrs old male came to the psychiatric OPD complaining of continuous, dull, non-progressive headache for the last 8 years. The patient has seen numerous neurologists in the belief that he has a brain tumor even though all his investigations have been normal. The patient insisted that he had a brain tumor and requested yet another workup. Psychiatric evaluation reveals disease conviction in the background of normal investigations. The most probable diagnosis is
Somatization disorder Somatoform pain disorder Hypochondriasis Conversion disorder