Sleeping like that seems to be a GSD thing. Also, that's not the best picture to tell if your pup is overweight. If he's having issue getting up, I'd have a vet check him out and have xrays done on his hips to see if that's the culprit.
5 month old. 54 lbs a week ago. Not overweight and sleeps alot also. His active times are early in the morning and around 7pm . He's at work with me right now and has been sleeping under my desk for the past hour. Only woke up to go play for 30 mins. He seems to sleep more now that its so hot here in Ca.