Thanks for your question. Sudden deafness is very uncommon in birds. Pet birds have a limited number of ways that they can show their illnesses, but these include decreased activity, decreased appetite, and decreased interaction with family members. Parakeets, or budgies, are very small birds and thus small changes in their usual routine are important to investigate.
A full physical exam of your pet by an experienced avian veterinarian is needed as soon as possible. You can call me at 813 885 4477. Dr. Peter Helmer