I think Frickaflip really hit the nail on the head. That combination of psychological and chemical dependency works like clockwork. In early recovery I get super antsy at around 4:30 and start feeling depressed if I don't drink. The lizard brain is basically releasing every single chemical it can to get what it wants. I've had mixed success with AA, but I did feel that attending some meetings in the early evening helped with this. It's basically a way to reconfigure the brain and create new neural pathways.
When it comes to booze I'm basically reduced to Pavlov's dog.