I have a princess parrotfish, who's slowly converting all my live rock to sand, but otherwise is doing quite well. He's a little more than half grown.
I'd read that they will sleep in a "mucous cocoon", but hadn't seen mine do it until this morning.
It had a bubble-like cocoon around it, with some sand stuck in it. When it broke it looked like a spider web or cobb web had grown around the rocks it had dug under to sleep.
I'm assuming this is a sign of good health, also.
I didn't have time to get a photo (was on the way out the door), but it was very cool to see.
Here'a pic from another site for those who are curious: