Yeah, codependency is definitely a sacrifice of the self for another person--to the point where there's very little separate self left.
Here's an example: My AH got out of the hospital on Friday, after having had an alcohol withdrawal grand mal seizure on Thursday. It was totally scary for me, never having witnessed one before. I called 911 in a total panic, not knowing if he was stroking out or having a heart attack or what.
The kids texted me at the hospital and asked me how he was doing. My "Codie Freudian slip" was in my response back: "Dad had a lot of tests. He'll get the full download from his doctor later but I seems to be fine." (Note I said "I" instead of "he.")
The classic joke is the codependent who, when drowning, sees their alcoholic's life pass before their eyes.