Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for Bruno. There actually could be several different explanations for his symptoms; there wouldn't necessarily be just one explanation for it:
1. The most common cause for his behavior is going to be tracheobronchitis (aka Kennel Cough) especially if he's already received all of his vaccines.
This condition is either secondary to a viral or bacterial infection and can be contagious between dogs. If a bacterial infection, then these dogs respond to oral antibiotics pretty quickly.
But if this is a virus , then it will have to run it's course....which is usually between 10-14 days. Kennel cough typically worsens before it gets better and gradually improves rather than abruptly stopping unless this is a bacterial infection and antibiotics are started.
Many of these patients will also run mild fevers. If you have a thermometer, you can take his temperature; normal is between 100 and 102.5
2. Canine influenza (canine flu) or even pneumonia can mimic kennel cough in the early stages but these dogs rapidly become sick. They stop eating and they're quite lethargic. These dogs should receive vet care sooner rather than later although it might take a day or so before symptoms develop.
3. Ingestion of objects such as sticks or rawhide, grass, or anything that could cause damage to the back of the throat when ingested. If this is the problem, then it should resolve pretty quickly…usually within just a few days. I recommend a diet of soft or moistened food (avoid dry kibble) so that further damage/irritation is avoided.
However, I wouldn't expect him to be acting "off".
4. There are other conditions which might cause these symptoms but are typically seen in older dogs such as a collapsing trachea or heart/lung disease.
As to over the counter treatment options, cough suppressants can be given although I'm often hesitant to use them if kennel cough (#1) is the problem. I want those secretions removed from the upper airways and I rarely want to inhibit this reflex.
But acceptable ones to use include Dextromethorphan (http://www.petplace.com/article/drug-library/library/over-the-counter/dextromethorphan-robitussin-dm)
The dose would be 0.25 to 1 mg/lb 2-3 times a day. You just want to double check labels and ensure that the formulations only contain this ingredient although inclusion of Guaifensin is fine.
If he continues to choke/gag and/or becomes really lethargic and/or doesn't want to eat, then a vet visit may be prudent.
I hope this helps and that he's feeling better soon. Deb