Society Finch sick?

Question
I have a society finch who for the past 24 hours has been very lethargic, puffed up and is now off balance. Still eating and drinking but the balance problems are becoming more pronounced every hour.

Answer
It may be air sac mites. The best way to tell is to hold your bird up to your ear and listen for clicking. If you hear clicking, the website provided offers Scatt which kills air sac mites.
If you don't hear clicking, take a look at her nasal passage and her vent. If her nostrils are running, it is best to take her to the vet to get some antibiotics to get her healthy. If her vent is yellow, again take her to the vet to get medicine.
Is the finch a female or male? If the finch is a female, it may be a wind egg. These are almost always fatal but wrapping the bird up in soft fabric and laying the fabric and bird on the bottom of a small, heated cage, MAY help the bird pass the egg.
If the bird is a male or no other cage is available, get heat on the bird NOW. Sick birds should have a cage temperature of 31C. I find the easiest way is to use an infrared heat lamp from the reptile section of the pet store. Wrap up three sides of the cage is a towel and watch the temperature closely; you don't want the temperature to go over 31C. This will help lessen the stress the bird is under and give them a chance of survival.