I think it's a mix of dehydration and stress. I work at a gym part time (what I actually want to do) and we got a ton of new equipment and as I messed up my hand the other week I had to work one handed. I don't think I ate/drank enough water to make up for it as I pretty much collapsed on the bed when I got home.
Still, not missing this feeling!
I even checked my bin for cans to ensure I hadn't gone mad and imagined the last sober week.