Boy HOWDY, but yes I know exactly what you are saying! :DFor me, coming in to work on Monday is rest sometimes, comparatively speaking. I think the thing is that (for me) when I am performing, I am doing more than simply singing (like I would for myself in the car or the shower). I am exerting more energy to try and connect with the audience, and to drive the music or emote so that it is not "just another rendition" of whatever.
What helps for me is to try and keep rested. No hard parties after a long gig. No staying up late to see a film after performing. And I schedule some time off from work if we're doing a weekend long (or more) gig, or after an away trip.