This is hard to explain because of restriction of posting links here but I'll try. (I might add screenshots afterwards, maybe somebody will notice and name the spell/disease on my character)
The problem is that I have black mist/ethereal/cloudy hovering on my character all the time.
I think the problem occured on time of the Dawnguard quests inside Castle Volkihar, I clicked the Bloodstone Chalice located in one of the rooms just out of curiosity, (not as an vampire)
there was no message or anything else but afterwards I nocited this black ethereal effect on my character. The effect is because of this or something else that happened inside Castle Volkihar.
player.dispellallspells doesnt work.
setstage eafd5 10 doesnt work.
Showracemenu disables the effect but when saving and loading after that, the effect comes back.
And no, I dont think its because of any mod. If I disable Dawnguard.esm the effect goes away...