I just picked up Rocket this afternoon after a week of boarding. He gets turned out 5-6 times a day with several other greys and has acres of fenced land to run on there. They told me that he went running with 2 of the other dogs every time they went outside.
He came home exhausted. I fed him his dinner, and he went straight to bed afterward. He has a huge grin on his face, so I know that he is zonked and in a deep sleep. It will take him a few days to get back to his normal routine. If I didn't know that he was tired, I would describe his behavior almost exactly as you are describing.