Well, I'm not sure. The symptoms of Infectious Laryngotracheitis (ILT), as found in Gail Damerow's Chicken Health Handbook, are:
Watery, inflamed eyes, swollen sinuses, nasal discharge, unthriftiness, coughing (that sometimes produces bloody mucus), head shaking, breathing through mouth, gasping, choking, gurgling, rattling, and whistling. The disease is acute, but spreads slowly.
Your bird only exhibits (from what I can gather) the coughing, sneezing, and wheezing, though it did come on suddenly. ILT is fairly common, especially at poultry shows, and probably, poultry swaps. Mortality is 10-20% on average, but can be higher in an acute infection or in mature birds in wintertime.
Infectious Bronchitis is just as likely. It causes (from the Chicken Health Handbook):
Gasping, coughing, sneezing, rattling, wet eyes, nasal discharge, loss of appetite, swollen wattles, and sometimes, swollen sinuses.
Infectious Bronchitis is just as common, if not more common, than ILT. The only real difference is no bloody mucus, and the fact that Infectious Bronchitis spreads faster and easier. So, I'm not sure which disease your bird has. Since both are viral, the treatment is the same (keep bird warm, well fed, hydrated, and stress-free). Personally, I think that your chicken has Infectious Bronchitis.
Survivors of Infectious Bronchitis are immune to further infections. However, they will be carriers. ILT survivors will also be immune, but carriers. If you want to keep your bird, you should vaccinate all of your other chickens for ILT. This will, at least, prevent them from being infected. ILT is a reportable disease in some states, as it is very serious.
So, give your bird the supportive treatment I wrote about above. It would also be a good idea to get Oxytetracycline (sold under names such as Duramycin, Tetroxy HCA-280, LA200, or Terramycin). Give this to your chicken to prevent secondary infection. A secondary infection of Chronic Respiratory Disease is especially prevalent in birds with Infectious Bronchitis.