Weird hump

So I noticed a few days ago a hump on the back of the neck of my adf. I think it wasn't as big as now, so it concerns me. Yesterday they got beef heart, so I thought that maybe he got a bigger piece and couldn't swallow it properly, but he swims well and seems fine. Today when I fed them again with tubifex worms, he ate, but it seems like he regurgitated some of them and then tried to eat them again.