He has a history of drug and alcohol abuse, so it's possible that he relapsed and went on a bender.

Important to note that I haven't seen anything to say that he had any drugs or alcohol in his system. I haven't read any of the reports. Maybe someone has already done the test and said there wasn't any drugs or alcohol in his blood.

One thing that sucks about him dying in a fire is that it may frustrate efforts at toxicology/autopsy.