this is a relatively new issue with us. It started two weeks ago during Beck's training class. Admittedly, it's a bit boring for him because he knows the stuff that the dogs are being taught, but I still thought it would be another opportunity for socialization and stuff...anyway- last week we were doing long lead recalls. Beck fell asleep waiting for his turn. When I finally woke him up (and it took some effort) he did his recall just fine, but instead of running at breakneck speed back to me like the instructor wanted, he just sort of loped to me, then laid down again and got all comfy and started to fall asleep again.
Then, the next day DH and I decided we would take him to a really busy place and work with him on not jumping up to greet strangers, so we sat outside a large bookstore with him, with dozens of people coming and going. A good number of them came up to greet him, but after about 15 minutes of that he laid down in the middle of the sidewalk and fell sound asleep.
I called the vet, she said he's fine, just a bit lazy & to be thankful that at 6 months he can relax enough to fall asleep around people, but I have never in my life had a dog like this lol