Same thing happened to me a couple nights ago. Probably brain in but I'm definitely in a honeymoon phase with the HD800. New tubes, new cables so who knows what is going on. Enjoying them much more than in the beginning, which was about a month ago but realistically I've been listening only for half that time.
Not sure what it is but 3 nites ago, i started listening to my favorite albums on the HD800 and instantly recognized the change in the lows. Immediately, I switched over to HE500/Emo to compare and did confirm the clear increase of bass on the HD800/WA22. Whatever happened! I like it.