I have this tendency to either completely starve myself when I am doing something, or to overindulge in rich foods for a long period of time.
I see it as an awareness but devaluing of Si.
A Si role or PoLR type would not be aware that they were hungry; they would forget about their bodily needs. But because I am totally aware, and am actually restraining myself, it points to Si devaluing, but competency in it.
Overindulgence may seem like a Si unaware thing, but it's not that I'm overindulging without being aware of my bodily state; I'm entirely aware of it. I just want to satiate my desire for nice things.
This on/off quality probably has a lot to do with being an Eight - there has been Enneagram literature which has talked about the counterpassions of each type; they Eight's being Waryness (to match the passion of Excess). Since they spend a lot of time being all out, excessive and lustful, they often feel the need to balance it out, and they will be extremely hard on themselves in terms of their needs, and in terms of their outward behaviour. Little do they know, in trying to counter their excesses, they are being excessive in limiting themselves as they do. So, ironically, in attempting Waryness they end up latching onto their passion of Excess, but simply in a different way. (For those who are interested in the counterpassions, I'm creating a thread in the Enneagram subforum.)
What are your experiences with this kind of thing?