I never post here either but totally do that too. Sleep deprivation used to be one way for me to purge too but i wont go into the details. But I totally think sleep depriving yourself and making yourself be hungry is self harm. In a broader sense, I also think it's got to do with dissociating from your body. Like, you're not your body--you can do whatever you want to it--make it stay up, keep it from eating when it's hungry. It's a punishment thing, at least for me.