We have had Guinea pigs a few years now. One was the oldest at 3 yrs who had a cage mate probably 2yrs now. The elder passed away very ubruptly. Very lethargic and rushed to emergency vet at night, however they wouldn’t treat because they only do cat/dog. Suggested honey and warm until vet could see in morning, well she didnt make it. You get was doing fine. Purchased another cage mate from store, youngin. Placed in same cage after introduction for the solo girl now. And 4 days later that one turns up dead too. No traumas. What the heck? Other one still seems fine.