It could be the bendryl, I recommend calling the vet for instructions on handling this. They may reduce the dosage, or your glider may adjust and be less groggy over time. I gave my dog benedryl every night for a while, and it began to have less effect on her. I did stop it for some time and will begin again when she appears to develop symptoms again.
I don't know why there are changes with your other glider, but mine have been acting like that recently, but they've also been waking up a bit later after first eating, and seem less playful until much later, but then I have to go to bed. They're still getting out for a little bit, but they go back in their cage soon after and are not doing much. They haven't been to the vets recently, so it's not that. I know they kind of change their routines seasonally and also as they get older, so I'm feeling it's more likely that for my trio, they are acting well otherwise, still very active later at night and super early morning.