Neck/Shoulders swollen after Tooth Cleaning

My cat Ozzy (~6 yo male, 14 lbs, ?asian bobtail?) had a tooth cleaning on Friday. He was sent home with with 3 doses of meloxidyl for pain, which we finished on Monday. As of last evening (Tuesday), his shoulders felt stiff. This morning, the swelling seems to have spread to his head? When I pet him in these areas it feels like air is being released under his skin, and it sounds like rice krispies. I've been trying to avoid petting him because I don't want to hurt him (i dont know if this hurts him or not). But I'm nervous about what this is, but don't want to freak out if it's not an emergency.

He's eating less and he's somewhat lethargic, but alert and wants company. I don't know of the swelling is affecting is ability to swallow or breathe at all. He's still drinking water and climbing cat trees. I assume he's feeling some post-procedure pain, but 4-5 days later seems unusual to me. There were no extractions.

He is currently on a calorie deficit for weight loss (he's down 1lb in one month) and has a history of bladder crystals, if that's any help.

(My local vet is closed today, hence why I'm initially reaching out here. We've called and left messages, but probably won't hear back until tomorrow morning.)

UPDATE: thanks, all. We got him seen. Vet doesn't believe the dental cleaning was related given the time-line, and no coughing. He was given an x-ray and definitely just saw gas under his skin, but no diagnosis for subcutaneous emphysema (his heart and lungs are normal). No fever. He was given a shot of antibiotics as well as a week of oral treatments assuming the air build up is caused by bacteria. How did the bacteria happen? Vet guesses a spider bite, but I'm curious if one of our other cats was showing dominance while I wasn't home and bit/scratched him. I can't find any wounds on him though.

Still a mystery, but hoping the antibiotics resolve it.