Not to scare you Jorge, but I have read certain infections will cause snakes throats/necks area to inflate with a bit of air, and makes it look full of air or puffy from inflation, but usually in only certain positions too. Have you treated it with Flagyl? or any other antibiotic?. This seems to happen more when their heads ar pointed down. I had an adult Yellow Rat pass away a year or so ago, and I recall he was doing that some prior to going downhill before treatment could help him.
Like say he is hanging on your arm, and about a foot of his front portion is out and slightly downward, this is when the "inflated" look usually begins to happen. It is said to be caused by when the snake is in that particular position, the glottis is more restricted so it fills some with air as it breaths, but some tends to stay to give the puffy look.
Now I'm not saying it is this for sure, but I don't want something bad to happen to one of your nice animals, know what I mean?.
~Doug
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"a snake in the grass is a GOOD thing" 
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