They can inflate. I have heard of air being trapped and actually kind of massaging the air out buy holding the fish and rubbing your finger up the belly. I have a blue spot as well but have never seen that problem. Was just some info I had seen when researching the fish.
I've seen them do the inappropriate swallowing of snails. I've also seen them look pretty fat like that after a large meal. Similar, but not. I'd wait to see if it goes down in a day or two. If it's food related (snail/hermit or not) it should work it's way through by then.