Been absent for a while

And I'm going to be honest, I've fallen off the wagon a little and I'm feeling pretty low.

I've been thinking a lot.

Sometimes it feels like there's this nasty, uncontrollable little part of me which constantly feels the need to self destruct. When I was thin, I saw not eating and getting skinny as a punishment. So I did it, and lost a lot of weight.
Now that I'm bigger however, I've completely romanticised and glorified being skinny. So now to me, it's a reward, it's like being starving and underweight has become a thing that only someone who deserves it can have, and a thing to be desired like having perfect hair or amazing skin. So this little self-destruct part is doing things to keep it out of reach. I feel totally like it isn't even me raiding the cupboards and stuffing my face, and afterwards I feel utter guilt. And despite the guilt and shame, it's like this self destructive part, this nasty little creature in my brain feels totally self-satisfied and smug. Like it got its way and will now leave me alone for a little while.

To keep this evil part of me content and quiet I used to starve and purge and destroy myself by getting thinner and thinner. But now my mentality has changed and I am completely in love with the idea of being skinny, this part of me is more angry and scratching me from the inside when I manage to resist food and exercise more.

I know it sounds totally nuts, and I know it's my own mind thinking these things, not a separate entity. But it just feels like whatever I decide will make me happy, this strange part of me just does everything it can to fuck it up. So when I thought eating and having a regular sized body was healthy and fine, it made me starve. Now that I'm more in the mindset of "the thinner the better", it's pushing me to eat more and move less.

Even just weird stuff like, I want better skin and know that drinking water can help this. And I never ever drink enough water, sometimes I'll sit there feeling horribly thirsty and just not get myself a drink. I am always dehydrated yet I'll still restrict my fluid intake without even realising or meaning to. What does that mean? It's not going to make me look or feel any better, if anything it will just make me bloat and dry out my skin, hair and nails. So why do I do that?

I keep getting water infections because when I need to pee I hold it in for as long as possible. And I know it's a stupid thing to do but I still do it, and I really really don't know why.

Why are all these self destructive habits happening even though I know better? And why do I feel like it's another part of me, this clinging little creature that got inside my head one day and fed off me until it became strong enough to force me to let it take over?

Am I crazy?