why does it keep fucking lagging me out and closing the game...

happened in candlyland yesterday
tomb and trench

and just fucking now, i was attempting my first oryx solo, and had him down to ~20k health

the game just shuts down and goes to the menu... no lagg beforehand or anything..

I've had this happen multiple times, though not at these crappy situations. More like picking up potions.
I would also like a fix..