That reminds me of one time when I went to tuck our beardie in for the night. If I'm still awake by then myself, my usual procedure is to pet him a little, and if he does his little snuggle up/dig in maneuver, I figure he's already done for the day and doesn't want to be disturbed, so I just cover him up and turn off the lights, but if he still seems wide awake, then we do a bedtime cuddle.
This particular time he already looked like he was asleep, and he had faded out to a light golden color, and when I petted him he didn't move at all. He's ADV positive and I had read that sometimes this can cause them to die suddenly for no apparent reason, so I watched the area behind his arms for a little while, looking for any signs of breathing. I didn't see any movement, so then I thought about trying a little more aggressively to wake him up, but he looked so beautiful and so peaceful that I decided to just assume that everything was alright one way or another and just let him be. I was still worried when I went to check on him the next morning, and then I saw him blink. Phew! :mrgreen: He's still alive and still apparently doing ok.
That third eyelid scares a lot of people.