Guinea Pig

Question
Hello,
I have a male guinea pig around 3 years old and just recently started to look unsteady on his feet and keeps stopping to lay down. Whenever his head is lifted up it slowly starts drooping to the ground and he's not interested in his food. I've taken him to the vet and the lady said he looked healthy in terms of body temperature and physically she didn't feel anything abnormal apart from his stomach being empty. She gave him some fluid and an injection to help stimulate his digestive system. I was given some powered food to mix with water and force feed him every couple of hours, but other than that i'm not exactly sure what the problem is and the vet didn't really know either. It's the second day and he's nibbling on some cucumber and grass on his own now but still just laying around. I'm just curious whether you may have come across something like this and maybe know what it may be? He doesn't seem out of the woods just yet and the vet just said 'fingers crossed'.
Thank you in advance for your time in reading this and getting back to me :)

Answer
My first inclination is to wonder how old your little guy is.  When you say "around 3" I am wondering if perhaps he isn't a little older than that and what you are experiencing is the beginning of the end of his lifespan.

The typical age for a guinea pig is approximately 5 yrs.  However, I've had pigs that passed when they were just barely 4, and by contrast my oldest was 7 1/2 yrs.  As with people they age differently.

Given the fact that the vet could find no abnormality that could explain this, it seems that perhaps he has just reach as far as his life would take him. When they begin to fail they exhibit the symptoms you are describing. Assuming the vet did check his teeth, his empty stomach is another sign of his failing.

I'm sure this doesn't give you any comfort, and I'm so sorry I can't offer more help and good news for you. Our pets are never with us long enough no matter what their age. Please just take comfort in knowing he is not likely suffering or in pain. He's just reaching the end of his road.