the chinchilla might have pneumonia,that is a serious condition that a vet should check out,the symptoms are runny eyes,runny nose,loss of appetite,and stopped grooming,give the chinchilla plenty of fluids and take him to the vet.
I'm sorry I don't know much about chinchillas except they're beautiful and have very dense fur. All I can suggest is taking him to a vet. The sudden temperature change from warm to fairly cool at 65 degrees may have done something. Or it may be a coincidence. But lethargy, weepy eyes and diarrhea require a vet. Call around and check prices for an exam.