So, I am playing a battlemage of sorts. And I think I just found an interesting bug.
I suddenly realised that my magicka regeneration was through the roof, I could spam fireballs and ward myself seemingly forever,
so I searched my active effects for the cause of this, and found an effect that said something like this: Drain Magicka, +25 Fortify magicka regen, 1hour.
That effect have now worn off and my magic abilities reduced to mundane levels.