Sudden blood and pain?

So my cycles are pretty long and varied, usually ranging from 8 to 12 weeks in length. I'm not expected to have my next period until January 12th. Last night I suddenly started bleeding. There was no spotting or warning, just a gush of blood that soaked through my pants almost as soon as I felt it. The cramps started immediately. They are much more severe than any cramping I usually have, they almost feel like Braxton hick contractions. I've been curled around a heating pad all night and day, and I have a high pain tolerance and have never needed assistance for pms cramps before. The bleeding also seems to be heavier than my periods usually are.

Does anyone have any ideas what this could be or if I should be concerned enough to talk to a doctor?