My Little Roborovski Died

[Cotton]

My little Roborovski, Finnegan, died on Sunday. There was no indication he was ill or injured. He was active throughout his last night, running on his wheel. In his last week, I was excited that he suddenly started sitting in my hands. After his death, I checked him thoroughly and went through everything in his cage. There is nothing to indicate why he died. As far as I know, he was young...6-8 months old. I'm stuck in a loop, trying to figure out what happened to this adorable little guy.