I entered a Black Book, when i came back to Solstheim, my vision went blurry, and i started losing health - like standing in the pools when reading a black book.
I thought it was part of a quest - like using the books too much, and that i'd be able to eventually cure it.
I carried on and eventually lost the blurriness, but i still have health degeneration.
I now have to constantly heal myself to survive.
the kicker is, this is my most developed character, i've taken him to Level 72 - and am wanting to push to 75 to meet the Legendary Dragon and gain the achievement.
foolishly i saved over my saves before i contracted this bug.