Well you’re unlikely to be able to attend this course (if you are then you’re very lucky!), but if you want to read up on what the supernatural meant in the Middle Ages then I would recommend looking over the course notes for Eileen Joy’s The Medieval Supernatural.
I have created a page on this blog that captures the reading list as I just wanted to make sure I had all the suggestions recorded somewhere. In particular I would recommend the work of Robert Bartlett as a good introduction to the subject.
In a world which is indeed our world, the one we know . . . . there occurs an event which cannot be explained by the laws of this same familiar world. The person who experiences the event must opt for one of two possible solutions: either he is the victim of an illusion of the senses, of a product of the imagination — and the laws of the world then remain what they are; or else the event has indeed taken place, it is an integral part of reality — but then this reality is controlled by laws unknown to us.~ from Tzvetan Todorov, The Fantastic: A Structural Approach to a Literary Genre