I don't know the mechanics of it, but I believe blackouts are simply when the amount of alcohol consumed affects the processes in the brain that transfer short term memories into long term memories. A bit like the man in the Christopher Nolan film Memento if you've ever seen it, who has that condition due to an accident. So it's not like you go into a separate "blackout state" like a zombie or something. I've known people who seemed their normal (drunk) selves who would tell me the next day they can't remember anything after a certain point.
I used to suffer them all the time. I'd come back from the pub and watch Match of the Day, or the next episode of a box set I was watching, and the next day need to watch them again because I couldn't remember anything that happened in them after the first few minutes. The worst thing for me was often the point where the blackouts kicked in was about the same point that my behaviour was no longer what I would consider my own. I would say and do damaging things completely out of character. The shame the next day as I'd have to try and piece together what happened, dreading phone calls or texts from friends out of fear of what they'd say I'd done. A horrible, horrible feeling.
What I love best about sobriety is knowing that I can now own everything I say or do. It will all be coming from the real me. Doesn't mean I won't make any more mistakes in my life, but I'll at least understand what I was trying to do, and know they came from the right place.