Mickey and Leah both did that once too! It's unusual for a dog to 'disappear', but they did.
With Mickey, my hubbie called me from home (I was at work, of course - back in my days at the county hospital, where I pratically lived) to let me know he couldn't find Mickey (then still a puppy). Fortunately (or, actually, maybe unfortunately from a total perspective), we lived only 2 1/2 blocks from work, so I was able to clock out and go home. We searched the neighborhood; we asked everyone we saw... NOTHING! I was in tears and convinced someone had taken him (he was an adorable pup!). We finally gave up and hoped he would find his way home. Soon after we got home, out he came ... to this day, I have no idea where he was hiding, but we had called and called - so he had to have been fast asleep SOMEWHERE in the house.
Leah also disappeared when she was about 8 years old. My Mom and Dad were visiting, and I had let her out into our fenced yard. She would bark when she was ready to come back in, but this time, I realized it had been a while, and I hadn't heard her bark. I went to let her in, and she wasn't in the yard. The gate was closed and she wasn't a digger. Where was she? I called and called - no answer. I went through the neighborhood - NOTHING - no one had seen her. I was beside myself - thinking someone had stolen her from my yard (you hear about such things, you know), About an hour later, I heard her bark. I went to the door - NOTHING! Where was she? I called and listened, and she returned my call with a bark. ??????????? Finally it dawned on me. The area where we lived (in the 'Glades") had very rich soil (muck) that broke down and everyone had to fill their yard, but the houses were on supports down to the bedrock, so the soil would 'sink out' from under the houses. I looked, and sure enough, there was a hole leading beneath our house. I took my life in my hands (literally - snakes, spiders, other nasty stuff under there), along with a flashlight, and crawled down into the hole. I called for Leah, and she barked, but she must have thought she was in trouble, because she wouldn't come to me. I crawled further under the house and shined the flashlilght - there she was. I called and called, and she finally came to me JUST barely within reach. I grabbed her and dragged out out. Her ears were back and she was cringing - she just knew she was in trouble. I was so glad to see her, I couldn't even begin to scold her!! She never did go back under the house, although, I'm sure she could have found another way in if she'd wanted to (we blocked that hole immediately)