Sherry's horse "Rowdy" was bitten by a rattlesnake on his nose. The picture shows Rowdy after 3 days. The swelling is still quite visible. On the first day he looked like a Manatee. Luckily, Sherry had everything on hand to treat Rowdy with telephone instructions from the veterinarian. Attempts to get a plastic tube up Rowdy's nose were not successful; and although his breathing was affected, it was not critical.
Check with your veterinarian. He can advise you about the drugs and supplies to have on hand in the event that this happens to you.