I have A degu that is approximately 12 years Recently she was acting a little off and to tell the truth I really just thought she was dying of old age but she's a stubborn old bird and she never stopped eating and drinking she just looked bad and was breathing hard. so I decided that she had a respiratory infection I took her to the vet She's been on antibiotics for about a week And she does seem better but one day she'll be running around fine and the next minute I'll find her laying on her side and I think she's dead I touch or in 2 jumps up and takes off. I don't know what the deal is with this laying on the side thing never seen her do it before it's almost like if she gets on 1 side she can't right herself for some reason but it's weird so if anybody has have any kind of similar experiences please let me know. Like I said shes eating and drinking fine.
I'm impressed with the age of your degu! Well done!! Clearly you have cared for her well, and she is also blessed with some amazing genes. I am sorry that you are seeing signs of slowing down and potential end of life. Often when a degu lays on it side in such a manner that it looks dead . . . there are serious health issues going on . . . which you already know about and are in the process of treating. We do have a number of degus that like to sleep on their sides and scare their owners that way, as well. So . . . it's hard to say really, without just jumping to conclusions. The fact that she is eating and drinking fine are very encouraging! Is she peeing and pooping normally? Does she allow you to hold her well enough that you could hold her chest up to your ear like a phone and take a listen? Do you hear whistling in her nostrils . . . which could indicate trouble in the sinuses, such as infection, root enlongation/elodontoma, or a growth of some sort. Do you know if the vet checked your girls teeth and molars to see if there is any over growth or spurs?
Things that spring to mind are some kind of weakness from something like a stroke or some kind of blood sugar thing laying her out and making it difficult to move or maybe a consciousness issue or stiffness/pain issue, but the fact you can rouse her by touching and startling her is probably a positive thing. Heavy breathing could be her heart and lungs starting to fade or can also be a sign of pain, particularly if you see her hanging out in a different place.
Does she have a heatpad or cage heater? Most oldies get a lot of comfort from a heat source if you can provide one.
I would go back to the vet for a follow up and get them to have a feel all over her body for any masses and tell them as much as you can think of that could be relevant, they might be able to point in a certain direction that might help with a strategy to help her.