he wasn't gasping, he was taking water in his mouth to soften the food. My eel does this all the time, after eating, he will flair his mouth open repeatedly and take in water, after a bit, the small bulge of food slides down and disappears.
it's not him about to die, it's fairly common with some eels. Mine has done this a lot, and i see a bulge in his body as wel after feeding sometimes, and he's been alive for almost 3 years.