Chickens do get IBD (infectious bronchitis disease) that could cause the symptoms you mentioned. They become very congested, wheezy & ill for a few days and then quickly rebound in most cases. They do however, remain infectious for around 3 weeks. If it is EBD, the rest of your flock will also probably get it. Antibiotics do not really help except when you suspect the possibility of secondary infections like E-Coli. Supportive care is the only treatment. AFter the 3 weeks, birds do not become carriers and develop some immunity to the disease. IBD can attack the kidneys or joints in some cases, causing lameness if joints are affected and probably death if it effects the kidneys. This would show itself within about a week of initial symptoms. Bear in mind that other illnesses can also cause similar symtpoms in birds.