I am sure he was completely out. The drugs relaxed the muscles of his airway, hence the snoring and gasping.
Exactly. He was give n a large dose benzodiazepine to get him to sleep, then a slug of hydromorphone to prevent pain. He didn't "feel" a thing. Guaranteed.
Here's a news flash, about everyone "gasps" before dying. It's called agonal breathing.
This guy was very "humanely" put down.
Probably way more so than the vet described above for dogs.
Perhaps he suffered from sleep apnea.