Thanks for the reply. We definitely try to never leave bugs in overnight for the exact reason you stated. This little cricket just had managed to find a hiding spot. They're crafty, sometimes.
The beardie seems to be perfectly normal today, which is great. We've booked for a vet checkup anyway...
My ~5.5-month-old beardie lay down where it seemed he wanted to sleep tonight. My wife thought it was odd since he's never slept there before. When I looked at him, his eyes were still open, so he hadn't gone to sleep yet. I didn't immediately notice breathing (though I know their breathing...