The scary thing for me is I thought I hit bottom many times only to find I could take myself even lower. It is definitely an inside job. Sure outside circumstances can assist in taking you to that mental state of "I give up, I just can't do it anymore - HELP ME!" but you have to be ready.
I like the saying that you hit bottom when you stop digging. For me my TRUE bottom is death - the addict in me will just keep chasing that dream until it is truly over (at least in this world). That means I better put down the shovel and ask for help now before it is too late.