This was our dear fish a couple days ago. He was all sick and not getting enough air in his tank. But the superhero that is one Sarah Sirianni saved the day and the fish. We made sure his little tube that makes bubbles in the water was functioning and gave him some shelled frozen peas to eat. He's been on a steady diet of peas and is now perking up quite a lot. I looked on line to see if I could figure out what is wrong with him and he had a lot of symptoms of an issue with his swim bladder. I think that is this little bubble inside that helps him swim easier. Now since he has an extremely large head, he is bound to sit near the bottom sometimes but if he gets too much air in the bladder it makes it really hard to swim and makes him all lethargic. This can happen if he swallows too much air eating flakes off the top of the water and if he is constipated. :) Ha! A constipated fish.
So I found that the best remedies are sinking food so he doesn't get any more air in him, and peas to help with the constipation. So since peas sink, he is getting those for a few days till he seems better, and then I'll start adding in some sinking food as well.
I'm sure you are all thrilled by the news that he is on the mend and doubly sure that it was thrilling to read all about our little guys ailments. :)