A person goes to what is familiar, what is similar to the original abuse. She doesn't recognize it as dangerous so the abuse gets played out again. She will experience tremendous pain and bewilderment because she doesn't know she is defending herself from self knowledge. The pain, and the pain can permeate a life, is coming from the whole self. That self is in a terrible dilemma as it tries to survive by honoring the psychologically entrenched law.
All options seem desperate and hopeless.
And, of course, guilt and shame come because people in this situation think they should be able to live their lives much better than they do. So, if someone forces himself or herself to eat more than they can bear and then forces themselves to throw up, that's one level, a physical level, of experience. Yes, a person will throw up to relieve physical pain from gorging on too much food. But there's more to it. They want to get it all out.