My first Vizsla did that about 4 times in his life. He would wake me up because he needed to throw up. Then I would see the hives on him. I would give him Benadryl, and within a few hours they would go away. Your sounds a little different, because they also blister.
As a pup, he had to go to the ER, due to a honey bee sting. That's not something that would normally send a dog to the ER. But his whole face got huge, eye swelling shut, then mouth started to swell. Wasps did not affect him as much. No hives, but the place of the sting would stay swollen for a couple of days.
My young dog now shine, is very different. She catches wasps, and guessing gets stung quite often. The only time she ever had any swelling, was on the very first thing.
Each dog can react differently, to something they're allergic to. Without seeing what is happening to your pup, it's going to be very hard to narrow down. Is there anything you can think of, that it comes into contact with only at night.
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