How serious is it? Can get very serious, very quickly. Life threatening.
What is it?
How can I recognize it? Labored or noisy breathing or mucus coming from the nose is an early indicator of respiratory issues. If your chin is lethargic (laying still without hopping around) AND is gasping, this is more likely end stage life.
Do chins get it? Upper respiratory infections can happen by contact with people who have a cold, or from living in a damp, drafty environment. Could also be a symptom of pasteurella.
How do you treat it? Early stages where the chin is still active can be treated with prompt vet care. Your chin will need antibiotics. If you find your chin unresponsive and gasping, this means you've waited too long for intervention.
How can I avoid this happening? Be alert! Know your chin and watch for signs of change in behavior or other symptoms. Get vet care early to avoid more costly interventions or even death of your pet.