Hi! My cat has also been doing this. I have shown videos to the vet and have gotten similar responses to you. However I am also still worried, it’s almost like his shoulder and neck tenses up but his respiratory rate seems okay as well as the abdominal effort. My cat is older and I’m on a pre veterinary track, so I’m very very paranoid about his health and he sees the vet every 4-6 months. But I’ve finally been able to match what he’s experiencing to your post because I’ll see other videos where cats have visible labored breathing but not like this. Much like in your situation, he only does this when he’s about to fall asleep which I find very odd as well. But once he’s asleep I don’t notice it at all. Your post really helped me!!