Think about it. All day you swallow all kinds of things. Hot, cold, hard, soft, crispy, mushy. Most you don’t even notice on the way down. But an air bubble just HURTS. Why is that?
Hurt how? Does it feel like it’s stuck in your throat, or halfway down your chest, kinda like heartburn, but without the burn? Every now and then I’ll experience this as well, usually when I feel like I’m forced to swallow when I’m blasted in the face with hot air. I don’t have any answers for you, but I think I know what you’re talking about.
Hurts like it’s being forced the whole way down. Isn’t the esophagus stretchable? It’s kind of like mobile heartburn.
I’ve often wondered this, too. I’ve decided on my own (so not based on any kind of scientific investigation) that it’s only the big ones you notice, and they hurt. You likely swallow smaller air bubbles all day long, without any notice. But every once in a while, you get a volume of air that is larger than a normally-swallowed mass.
And maybe there’s something about the gaseous nature of air that doesn’t allow it to stretch the esophagus in quite the same way as something more massive. A big gulp of water might have the weight and “substance” to push the tube open on the way down and distribute itself over more length. But a big air bubble might be forced into a much more spherical shape by the elasticity of the esophageal walls, and end up going down much slower and with more stretching than water or food.
This is all just my own hypothesizing, and isn’t much better than random speculation.