What bedding are you keeping him on? Sometimes mites live in the bedding but as others have said if the cage is filthy then looks like thats why hes so bad...you noticed he was dieing last night but didnt do anything about it - but now at night you have taken a closer look to see what could be mites - when can you get him to a vet? Oh yes and clean his cage out - this wont kill him but staying in a dirty cage will!