My guinea pig is 3 weeks old and he was on his side and he looked dead because he didnt move...When i got him i noticed his heart was still active and he was warm so i researched like crazy and found out that he had URI, uris are almost always fatal (NOTE:Bacterial respiratory infections are a common problem among pet store pigs)
¡¡¡¡¡¡Keep reading if your guinea pig has this or just for precautions!!!!!!
If you see your guinea pig on its side and it looks dead but you see them slightly breathing he has a bacteria wich makes him have trouble breathing you can take him to the vet and have medicine for him but if you cant afford that take out your blender get fruits preferably watermelon and grapes blend it and give that to him with a plastic dropper hes weak so you are going to have to hold him open his mouth and basically force it down his throat (this is at 6 or 8 in the morning) then in the even at 12 or 2 depending when you started you are going to blend vegetables perferably carrots, celery, and letuce and get the plastic dropper and feed it to him and at 6 or 8 in the afternoon repeat the fruit step he will feel better and you can give him dry fruit or veggies once he feels better
You are gonna have to watch his every move for 2-3 days
Best of luck if this happens to your piglet and hope this helps you like it helped me
This happened this morning on june 20, 2016 and as you can see from the picture he is feeling much better and as a treat i give him fruits and veggies