I've made this mistake before, and I think it's understandable when you're in such deep distress, you truly slide into that mindset of "this is it so fuck it." But yes, it's good you know just how destructive that can be and how easy it is to underestimate the difficulty in actually CTBing. The aftermath of making destructive choices because you're figuring it won't matter soon can be pretty devastating, and so is the strategy of actively making your life worse, in hopes that you'll be driven to CTB. I stand by my opinion that that approach almost never works to eliminate the survival instinct.
As far as trying to curb this temptation, I would only offer that it's okay to let yourself slide into the black hole of apathy but don't stay there for too long, and try your best to redirect yourself the best you can. Even if you skip a day of brushing your teeth, it wouldn't be the end of the world, but you would probably respect yourself more if you got back into the routine, if only to know that you're in some kind of control when you feel like your life is utterly out of control. Probably seems like a shit consolation prize, but then again so is a life that's already ruined.