We Lost Vinnie

We're not sure what has happened but I found Vinnie dead in his cage this afternoon. He was just laying completely flat on the bottom of the cage. The boys weren't really phased but Alex and I are pretty upset. I started crying and it set off Alex. I had been feeding him lots of celery and carrots lately so I pray that didn't have anything to do with it. He was about 3-4 yrs old and was adopted from the local humane society. I guess average life span is 3-7 years. I researched that today. I feel terrible.