Step 1 : Introduction to the question "What is brontophobia?"
...Brontophobia causes sufferers to experience an undue anxiety when faced with the sound of thunder. This abnormal, persistent fear occurs even when the person realizes that the thunder poses no threat to them. If caught outdoors when thunder begins, the anxiety can be extreme. Indoors, they may go so far as to hide under beds or desks, in closets or behind sofas. Brontophobia is closely related to astraphobia, or the fear of thunderstorms. Source: MedicineNet.com