For both of you, not being there to see, I would still say they have a severe poultry respiratory infection. You can try the Duramycin-10 at the highest dose but you may need to switch to Tylan to stop the symptoms. If this is some form of MG or Coryza, the whole flock is at risk. You really need to practise extreme biosecurity right now. Please, please, please, remember, it's not just your birds that are sick, it's you as well. You can spread this to others by walking into a feed and grain store, a bank, any place. Keep it there by biosecurity and treat the symptoms as needed.
Chickens do not get colds. Unfortunately they get diseases. There are so many that have the symptoms so very similar, it is hard to know unless you have testing or are well versed in the subtle symptoms. Sinus infections are different and can mimic some of the diseases too, but don't infect the bird for life as the diseases do. That's not to say they won't come back, they might if the bird is prone to them due to genetics or whatever. If this is something like a MG or Coryza, the bird will carry it forever. The symptoms will go away but not the disease and stress can and will bring it back. These birds can also give it to everyone in the flock now and later.
