You get used to operating at such a high level of stress - and for such an extended period of time - that the day after GA feels. . .wrong.
There should be more to do "right now" - more than the inevitable press events, the follow-on training, the "how do I use all the stuff you gave me" explanations. The website is live, the product is shipping, the email campaigns are clicking away, and life goes on.
Your body gets used to the fear, the uncertainty, the impending sense of something about to go horribly, horribly wrong. But nothing did. Sure, Mistakes Were Made. But mistakes are always made. The cardinal sin wasn't committed (missing GA) and we managed to avoid an entire constallation of venial sins as well.
There's nothing to celebrate except the feeling of having lived through another one. We all know we released something special - something that's going to solve some pretty damned serious problems for thousands of customers - but we don't have time to do anything but settle in for the next release. That's called being a Fully Allocated Resource.
I've read that after a long night in the kitchen cooks like to get together, slurp down sushi and unseembly volumes of beer and sake, and talk about the evening. They celebrate what went well, lick their wounds if the kitchen melted down, and wonder why the hell that six-top decided to send their steaks back.
We should be like cooks, given the similarities between creating software and cooking meals. We should go find a bar, hurt a keg or two, and work through how we feel about what just happened. We'd be better for it.