Gape worm or something else?

So, my rooster (Willie Nelson) has been sneezing/coughing/gagging on and off today. I haven't seen them much over the past three days as I've been working long hours, but my husband says one of the chickens was making weird sounds two days ago so it could have been going on for a while.

He was eating and hanging out with his ladies like normal today, except a couple times when he seemed slightly freaked out about whatever was going on with his throat. We have one pullet who seems to be the caretaker and she came to his side once or twice, which makes me feel like I'm not just being paranoid. He also went and rested in the corner of the coop all by himself at one point, which seemed slightly out of character. At another time, he regurgitated his food and I inspected it. It was thick mucous and undigested rice he'd just been eating from the compost. He had been gulping down a lot of water before that. He's been swallowing a lot today (at non-eating times). This evening he started leaning his head way back and gaping his mouth and swallowing repeatedly, so I removed him from the coop for the night.

Last weekend I went overboard on increasing the ventilation in their coop and it was quite drafty. It's been sunny and warm up until yesterday so I wasn't too worried about not being able to fix it until today. Yesterday and today it got cool, windy, and rainy. So, that's one or two nights of a cold, draft coop. Maybe that's what caused it?

He wears a homemade rooster collar and just this morning I was thinking how well it's working. It was a bit loose a couple weeks ago, but I guess he's grown enough now that his crow sounded quieter. Regardless, I removed the collar when I quarantined him because I'm not sure what the problem is and I want to minimize the variables.

That's all the details I can think of at the moment. Thoughts?