That's not a good sign at all. If this doesn't improve by tomorrow I recommend an emergency vet visit. Obtain supplies for syringe feeding and instructions. Do not feed treats to a chinchilla that is not perfectly healthy. Feed only pellets and loose hay until this problem is resolved, or the syringe diet provided by your veterinarian. If you treat this aggressively you will have less chances of something really terrible happening. This is not normal and can be potentially quite dangerous. I also recommend separating both chinchillas putting cages in separate rooms. There is a slight possibility of an infectious sickness from the other chin at this point.
There can be contributing factors with this related to stress and diet. How is your environment in the room as far as noise, other pets, room temperature, and light levels? You may need to put the cages in separate rooms until you figure out the cause. What is Chico's background? Is he in a different cage or location? What has his diet been like?
