Can't stop yawning

I was up until well past 4 a.m. today working on something work-related-ish, and though I generally do still keep hours like that, I'm absofrackinglutely dead tired today. I thought I was PHYSICALLY GOING TO DIE on the way home from running errands, and when I got home, I fell immediately onto the bed, where I didn't sleep but instead yawned, like, every minute or so for the next hour. Seriously. WTF?

I can think of one thing that most surely would make me feel better, but it's so bad for me and I swore I wouldn't ...