How is Jimmy today? It sounds like he was frightened by something. Did you have anybody enter your home while you were out? Even loud noises from a neighbor that are not typical day to day noises could have frightened him. How about storms? Were there any severe storms in your area during the time you were out of the house?
Sometimes behavior like that can also indicate the onset of a medical problem. Some dogs, when not feeling well, will choose to hide away from everyone and not follow their normal routine. If he is still acting this way a once over at the vet wouldn't be a bad idea. If he was frightened by something he should be back to his normal self by now.