This bug occured when fighting Medreth and the cowled cronies:
When only Medreth was left the game slowed down immensely (I did not use the "slow" mechanic) with framerate drops and everything.
When Medreth finally hit the dirt the game instantaniously "fixed" itself and went back to normal speed and the framerate cleared up.
It was as if the game tried to process a lot of data, or perhaps memory got filled because the battle took quite some time (I was being dumb)
Additionally, here is some information about my PC that might be relevant:
BIOS Date: 08/29/13 11:00:49 Ver: 43.02