Further reading has revealed that I probably contracted Vampirism in a quest I did last week where I had to kill some vampires as a Mage and didn't realize I'd got it. Three days later, when I went to sleep at the Arcane University, I became a full blown Vampire and had a dream about being burried alive (I miss-remembered the dream above). Apparently it takes 3 days for the disease to become permanent.
Once before, when I was in the Fighter's Guild, I had gotten the disease and noticed it. So I drank a Cure Disease potion right away. You can cure Vampirism like that if you catch it early.



