i had the same issue with one of my cwds when i bought him..

he was at a yard sale in the cold in his old tank that has an open top.. he was freezing when i got him (he must've been there a good half a day or so.. he was skitterish and brown all the time which suggests his previous owners didnt handle him or treat him very well. i had a job getting him to eat and drink too and i was quite worried for a long time.

any chance you can take pics of this swelling?. If you put him in his tank, is it quiet? if you cover it up and leave a large water bowl in there does he move at all?