The writer's visit to the British Museum has a frightening effect on him. Explain in your own words

In a flashback, J. recollects how he once went to the British Museum to research a treatment for his hay fever, and after reading about diseases, convinced himself that he was suffering from every illness known to man except for housemaid’s knee. J.’s doctor, clearly recognizing the man's paranoia, prescribed him beefsteak, beer, walking, and good sleep habits, and urged him not to “stuff up your head with things you don’t understand” (10).