Ferret acting strange

Before I get into it, yes I will be making a vet appointment. I'm simply making this post to connect with people who may have had similar situations to help ease my mind.

My male ferret Earwig is about 4 years old, and is a bit on the chunky side. He's always had a spunky personality and has always been real playful, but in the past week or so I've noticed that he isn't playing or just idly walking around like he normally does. His breathing seems a bit fast, not panting or anything but faster than I think it should be when he's just laying there. It doesn't quite look like he has hind leg weakness, he walks normally on rugs but does slip on my concrete floors, which most of my ferrets do. He is eating and drinking but when I let them out he just seems to walk around for a minute and then go straight back to sleep. Even though he's a big ferret I feel like I can feel spine more than usual, I have four other ferrets and I can't feel their spines as intensely as I can feel his. My mind immediately jumps to insulinoma and adrenal disease, I really don't know much about either disease other than the surface level research I've done about them. I feel like it could also be because he's overweight? I'm trying to cut back their food, but I just can't keep his activity up and nothing seems to interest him. It doesn't even seem like he overeats but he is definitely more robust in the belly than my other ferrets, which also makes me worried that maybe he has a tumor. Again, I will be making a vet appointment but I just needed somewhere to get my thoughts out I guess.

In the video I'm just showing how he walks on concrete vs the rug, and then his belly size compared to his cage mate who is about the same age. You can see how he just seems to be lethargic, and he was sleeping before I woke him up just to get the video.