...the concept of a 'mental health day'.
I learned it while working on a US base for a while, and I've decided to give myself one today.
Work's been intense, changing body is intense, trying not to go mad and overspend is intense, I've put myself out to meet a lot of people, which I find draining outside of a work context - and I'm just pooped! I should be out tonight (got stuff to do every single night this week, argh), joining a local choir - but I've emailed them for a raincheck. I can join next week - and today, I can mentally pull the covers over my head. MMMMMMM.
I'm lucky that my job means I can do this.