I believe it was a heart attack he died of and had like a shitload of drugs in his system
I had actually heard that he had gotten himself cleaned up and was off the booze and drugs. However the insane amount of abuse that he subjected himself to in the 80s and 90s just weakened his body so much (especially his heart), that it wasn't too surprising that it gave out like that.
Of course I could be wrong, I'm just telling it like I heard it.