A phobia is an irrational and excessive fear reaction about anything which concerns you about your health. It could be normal bodily aches or pains, which causes you to misinterpret them and throw you into a panic situation that it might be something very serious. Unlike general anxiety disorders, a phobia is usually connected to something specific, like your health for example. It could take the form of a dread of cancer, or perhaps a brain tumor in your imagination.