It started maybe about 2 weeks ago, I'd go check on my Suggies and Ozzie (male) would be curled up while the rest are active, and I'd pick him up and he'd move really, really slow. After about 10 minutes or so he'd start to wander around a lot and I'd put him back in his cage, he'd start acting normal and he'd run in his wheel. Unfortunately, the lethargy lasts longer and longer as time goes on, it's to the point where he's almost never active and I pick him up and put him right next to the food and pet him to make sure he eats and I help him by his water bottle, but no matter my efforts, he remains on his side laying in a pouch.
It's been weeks? You've noticed him getting worse or acting differently and you posted here so you're concerned. Please take him to the vet. There's only one step down from completely lethargic.