Help with a sick fish

[BMahura]

A couple days ago my lawnmower blenny started acting very strange. usually as soon as i walk up to my tank he come to the glass to check out whats going on. He has been really shy and hiding in behind my rock structure. It also appears that he is breathing heavily and his mouth is constantly open. I usually feed his a little nori once a week but since ive been knowtising these things i put it out every day for him and he seems to be eating it. Any advice or if anybody knows what this might me?
Thanks.