I literally came here to post that his behaviour looks EXACTLY like how I was when I mixed alcohol with tranquillisers I was taking for anxiety and panic attacks a couple years back. I see people have already made the connection that Scott suffers from these issues and will be medicated for them, he said he feels particularly anxious before shows too so my guess is that before this one he was already drunk and then also took some tranquillisers to calm himself down. The combination of the 2 puts you in a zombie like state, just like this. He will also be on separate medication for his bi polar disorder don't forget, all these meds mixed with large amounts of booze and a depressed mind state would make him look, act and sound like this.
Of course this is all speculation on my part but I am speaking about my own personal experiences of mixing prescription drugs with alcohol and the effects it can have on you. What I'm trying to say is, in terms of his health (physical, not mental) this could look like something a lot worse than what it is so let's stop with all the death talk!
I think because of Scott's past with heroin a lot of people (including Richard Patrick) automatically assume he's using again. Whils nothing can be ruled out, ask yourself, did he EVER sound this bad when he was loaded on heroin?? Did he act like this?? No, he was a great performer back then so that's why I'm going with the alcohol/prescription theory. Plus he sounded fine a couple of nights ago at the other gig so it seems like these sort of zombie/drunken shows are isolated which again backs up my theory.