It appears to be about alcoholism; the situation the character (presumably Todd himself, being as he's had quite public substance abuse problems) is in would appear to be an alcoholic's anonymous meeting, and every chorus, he is asking "how did I get here?" - how did I get this bad?
The key to this meaning is really in the lines "So I threw one down and said 'thanks a lot'/As I thought to myself 'Well, here we go again'." - He just can't give it up, no matter how many meetings he goes to.
It appears to be about alcoholism; the situation the character (presumably Todd himself, being as he's had quite public substance abuse problems) is in would appear to be an alcoholic's anonymous meeting, and every chorus, he is asking "how did I get here?" - how did I get this bad?
The key to this meaning is really in the lines "So I threw one down and said 'thanks a lot'/As I thought to myself 'Well, here we go again'." - He just can't give it up, no matter how many meetings he goes to.