Fear is something that comes from your brain that builds up from growing fears of memories, and unpleasant past events. It’s the feeling of not being safe knowing it is always around and will not stop bothering you. Stories like "The House Taken Over" and "Fall of The House of Usher" prove this point.
Fear takes over the way the mind workers. Like from the "house of Usher" Usher goes crazy thinking he killed his sister leaving her to die. He goes insane not looking good and talking to himself. he becomes careless breaking thinks and he sees and hearing things (his sister). In "house Taken Over" the narrator thinks parts of the house are being taken over. Although we do not know if it was truly being taken over, his sister went along