Corys are strange and very playful. I have moss in my tank that I bought. It's very fluffy and airy and they like to crash into the middle of it at high speeds and just suspend themselves in it hanging. They have tought the other fish to do it and now all the fish like to crash into it and couch out on it. They dont do this to any of the other plants. It's like a fish bed. They love it and can nap in it for up to an hour at a time. Put some floating plants in the tank to keep them below and maybe they wont do that anymore. Alos maybe increase your oxygen by adding a larger filter or adding an airstone
i'm no pro but it almost sounds like he's stressed out have you checked out your water lvl's? i['d get your water tested and see if its all balanced out corys i've always found can be very finiky about their water quality atleast thats what i've noticed with personal experiance but thats the most common thing with fish gulping for air is stress due to water quality but this is only my experiance...
or even try ading a bit of salt to your water cory's love salted water!! i've always found they do 10x better in brac water then FW but hey take of this what you will man!
I agree with Butterfly cories usually don't like salt. Same thing, I agree with butterfly on why he is coming to the surface, it's because he doesn't have enough exygen and it's not good. In the their natural habitat when there water gets murky and there isn't enough oxygen they swim up to the surface and take some from the air since they have that ability. Eventually he might die from lack of oxygen. I would do what Butterfly said or put an air stone in. Just my opinion