Another contender for The Bouncer Cup over here!
Yes I see my lowest weight and think, "One little cookie/chocolate bar won't hurt, look I'm xxxlbs!!!" Then of course it does hurt!
Like in your siggy, I have to decide that I want to be xlbs MORE than I am afraid of being xlbs. I'm so freaked that I might bump into someone more attractive than the man I'm with, someone who's more "elligible" in society's views, someone who matches (or will match) me on the attractiveness scale. (That sounds harsh, but I've only got my eyes open

) And I'm scared that I will be tempted. I know in reality that I probably wouldn't be tempted, or that there really is no-one better than the man I have now, but I think this is just a personal issue. I'm also freaked about unwanted attention because I've had quite a bit of scary stalker men talk to me and follow me around and just don't have the word NO in their vocabulary! However when I tie my weightloss/fitness with being a black belt, then I WANT to be there and be slim and I'm not afraid because I have those defensive skills.
I also think some reason for bouncing around is that we get complacent (good thread about that!), for example this weekend I saw a lot of people who haven't seen me for a long time and it felt good and I got complacent.

I KNOW I'm not at my slimmest right now, but I thought I could allow myself some bakery treats because EVERYONE ELSE thinks I'm slim. If only they saw me 4 or 5 weeks ago!
Just my take on things, I think self-sabotage reasons are worth working out. I found a book called "Why do you overeat if all you really want is to be slim?" I flicked through it in the book shop and I've ordered it from Amazon. I think it will be enlightening!