My friend originally had a young baby dragon (5 weeks old) when he moved in. About a week or two after moving in one day while I was out he called and said he couldn't find the little guy, had been looking all day, and was going to give up and go to bed, and asked me to make sure I didn't step on him when I got home. When I got home I very carefully turned on all the lights in the house, grabbed a flashlight, and first place I looked was a corner where all the dragons liked to go to, the last place the sun disappeared from in my condo as it moved across the sky. He was just a little thing, but there he was, all curled up fast asleep right where I was expecting him.
The other week I let the big girl out of my sight after she climbed off a piece of furniture and jumped to the floor. Half an hour later it struck me that I had no clue where she was. After making sure she was indeed nowhere to be seen I checked under the couch, then under the TV Stand. She was square in the middle of the crawl space under the TV Stand, once again all curled up and out like a light.
About a week before that the big boy had done something similar. I actually had to search for him, but I found him behind the couch, where I have a couple thin storage boxes hidden (he was between the boxes, asleep).
My friend lost Trooper (the big boy) once at another friend's house, he was convinced the cat had gotten the lizard and eaten it. Six days later while sitting in his room he heard the scurrying of little claws, looked up, and Trooper came running into the room out of the blue, stopped, and looked at him like "Well, don't you have any crickets?"
They'll get away from time to time, and when they do they're looking for somewhere small and quiet to fall asleep in until they get hungry. It doesn't necessarily make you a terrible owner, you just had a brain-dead moment. Check corners, crachs, and anywhere else dark and cool a lizard could get in to. Good luck!