What Happened? Here's what I think happened. You set yourself up to fail.

First you didn't take care of yourself during the day and then to boot, drank a significant amount of alcohol. Alcohol reduces one's ability to make good decisions and lowers inhibitions. It impairs judgement. Look at how bad you feel about eating what you did.

Now, stop beating up on yourself. You're back and hopefully learned a lesson about what not to do.