Oh I'm a bigger worrier with my babies even when well. So I understand. Its stressful.
The stress from Visiting a veterinarian even when they are normal can throw them off yes.
Of course taking extra naps can indicate they aren't feeling well too.
Offer all the favorites, like millet spray.
If I understand, yours didn't have a lot of symptoms, just smelly breath right? Had been eating fine, not napping extra before right? Good poops?
So right now we dint know what's wrong, or if anything is wrong. And you are going back to veterinarian on Tuesday. You can always call first thing Monday.
What I recommend is Xtra warmth. I like the sweeter heater as sold on Amazon. Sick burds really benefit from Xtra warmth 80-90 f . You can make your home a little warmer.
Keep them calm and caged except when out for cuddling with you .
Sick burds get whatever they want to eat within reason. No sugary foods. Try and keep diet healthy and what they normally eat. But hang a treat stick and/or millet spray. If seed mix is part of the diet bump up a little more than what you normally offer. If seeds are normally just for treats offer a few. Offering tge veggies high in beta carotene/ Vitamin A as that helps with immunity. Like warm cooked sweet potatoes, warm roasted or steamed carrots, leafy greens like romaine are higher in vitamin A and the yellow/orange/red bell pepper..sick burds generally burn more calories when sick up to 3x more. And often eat less, so you want to keep them eating and tempted.
Its a good idea to have a digital scale and track weight.
Those are just good supporting measures for Sick burds.
Keep calm.
If anything changes that has you worried , stops eating, staying fluffed and nit moving around, big liquid still with no formed fecal ( diarrhea) changes in breathing or anything then you would want to get him in and not wait till Tuesday.
But hopefully he is going to be just fine